There are three drag & drop easter eggs in your computer: The Breakout game gave credit to those who made System 7.5. The Apple Headquarters egg commemorated those who created System 7.5.2, and then System 7.5.3. And the Secret ROM Image was a gift to those who created the first PCI Macs.
The first two are Apple's most widely known easter eggs and are commonly referred to as "secret about boxes". Because of that, I figured it would only be appropriate to dedicate an entire chapter of my file to the eggs that made Apple well known for its hidden screens. The Secret ROM Image is sure to also become well known in the future. Below is the most comprehensive description of the secret about boxes you will find anywhere. If you have any further information behind these eggs, I would be happy to add it to this collection.
First, let me clear up one thing: The "Headquaters" egg was intended, at first, to work on all MacRISC machines, which are basically PCI PowerMacs. Since it is most widely referred to as a "PCI Mac egg", I will leave it at that. Second, you must have the clippings extension installed for the drag & drop eggs to work.
Breakout Game 
Note: Works in System 7.5 Only
If you type secret about box in Stickies, or any program that has drag and drop capabilities, and drag it to the desktop you will find yourself playing a hidden Breakout game with credits on the bricks to those that made System 7.5. The object is to knock a ball into the bricks and eliminate them without letting the ball go past your paddle. However, in this game you have unlimited lives and the game starts over again once you beat it. Each time you play, the names will move.
Breakout Game Desk Accessory Trick
Note: Taken out of System 7.5.3
You can get that about box from 7.5 into 7.5.1. It is a bit confusing but if you follow these directions closely you should be able to play the breakout game right from a desk accessory. Here's how:
First, copy a small DA such as the Calculator and rename it "Secret About Box." Next, use ResEdit to open both the System File and the Secret About Box desk accessory. Now copy the contents of the timd resource ID 12 in the System File into the DRVR resource ID 12 of the desk accessory. To do this, double click the timd resource icon in the System Files and select resource ID 12. Then choose Open Using Hex Editor from the Resource menu. Next choose Select All from the Edit menu followed by Copy. Now double-click the driver resource ID 12, and choose Open Using Hex Editor from the Resource menu. Choose Select All, followed by Paste. Save your changes in the DA and Quit ResEdit. You now have your own Secret About Box desk accessory. By William S. Peters in the November '95 issue of MacWorld. Page 146.
Or... All you need to do is drag the "System 7.5 Update" file out of the System Folder and restart. You are now running under System 7.5.
Ô£øBreakout Game on a PCI Mac
From: Jon Fullmer (jon@amembal.com)
This egg is probably only known among a few Mac users out there. Take your "Secret About Box" Desk Accessory created in 7.5.1 (follow the directions above), put it on a disk, and bring it to a computer that came with System 7.5.2 and has System 7.5.2 installed (all early PCI Macs); then play. There are no major changes but instead of the dedication being there for those who made System 7.5, it is for those who made System 7.5.2.
This egg is definitely very clever, and I applaud all the Apple engineers that thought of it.
Warning! - Techie Note: There is an ID 28 of the 'timd' resource in the System of a normal non-PCI Mac with no name or information. This same ID is in the "System 7.5.2 Update" file, but this time it has a name, "Who". This has drawn me to believe that that ID may be the source of the code for the Breakout game egg on the PCI macs.
Ô£øThe History of Breakout
There is some history that may tie into the Breakout easter egg:
Steve Jobs was of the first 50 employees at Atari, a Silicon Valley game company. Atari developed an incredibly famous game by the name of Pong, a simple electronic version of ping-pong. Nolan Bushnell, the company's founder, was eager to come up with a successor. He envisioned Breakout, the same type of game you play on your computer with System 7.5.
Steve Jobs was asked to create the circuitry of the game. Jobs had soon realized he had gone over his head and asked Steve Wozniak for some help. (If you don't know yet, Steve and Woz started Apple.) Woz agreed and created the game in four days with very few chips. His design for Breakout was so brilliant that none of the Atari engineers, including Jobs, could figure out exactly how it worked, which made it impossible to test, so the entire thing had to be redesigned in-house before it shipped.
There is a bit more to this story that eventually made some things go sour between Jobs and Woz, but you will need to read about that in The Mac Bathroom Reader.
Apple Headquarters
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System 7.5.2: Marconi (named after Gugliemo Marconi, 19th century Italian engineer)
From: Ronald Bruck (bruck@mtha.usc.edu) and James Renken
Important Note: QuickDraw 3D is not needed for this egg.
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On any PCI Power Mac, or any computer with System version 7.5.5 to 7.6.1, if you type secret about box (no capitals) in a text application that supports drag and drop, and drag the text to the desktop, you will see a picture of the Apple headquarters and a flag in the foreground, with the logo "iguana iguana powersurgius" (PowerSurge was the code name for the PCI Macs).
By moving the mouse around you control the direction the waves. In fact, you can make it break off, fluttering toward the ground and off the screen. The best way to get the flag to come off is to "whip" it back and forth (by moving the mouse up and down, at the right of the screen) and at just the right level of violence, it breaks off.
Using the codes given below, there is an easy way to make the
flag come off. If you show the mouse coordinates (holding
down W....), set the mouse to '0,0' and let the flag stop
waving. Then pull the mouse quickly to the right and then
move it up and down very rapidly. Once the flag is off, you can control the direction of drift with the mouse.
 
The name of the iguana on the flag is
Herman, and he is a 3.5-foot-long reptile
that lives in the cube of Dave Evans, one
of the OS engineers in R&D. He was the
mascot for Marconi (System 7.5.2).
Herman, not Dave.
If you wait long enough, the picture on the
flag will change to a picture of the development team.
Text scrolls by at the bottom saying "Watch out for low-flying iguanas". Credits follow.
Other Options
If you drag the text "secret about box" onto the desktop while holding these keys (American keyboard layout), you get different results (push the key after you start dragging the text):
•If you hold p, you will see a picture of the design team, with an iguana in their laps, on the flag. However, in System 7.5.3 holding down p will produce the MacOS picture.
•If you hold q, you will see a pink flag and blank background with a message that QuickTime must be installed to see images.
• If you hold down w, you get a dialog in the upper left hand corner displaying the coordinates of the mouse.
•If you hold down t, you get a dialog showing the frames per second,
which changes while the flag is waving.
•Holding down the the s key will eliminate the credits.
From: Rafi Goldberg (RafiMG@aol.com)
Note: You can combine these keys for multiple effects. Ô£øAlso, the keys in other countries vary due to different keyboard layouts. For example, pressing 'Q' on an American keyboard would mean a person in France would have to press 'A' to have the same effect.
Thanks to David Creech (d-creech@uiuc.edu) for help with the keys!
Ô£øWhat some of the Scrolling Text Means:
There are very random phrases and credits scrolling at the bottom of the System 7.5.3 Headquarters secret about box. Here is the inside scoop on the relationship between some of the text and the new desktop patterns, from an Apple engineer:
"For 7.5.3 on PCI PowerMacs only, there are a bunch of new desktop patterns. Since a bunch of the previous patterns are lame, hideous, or both, we decided to make some more. They are pictures of things around the R&D campus, like the sidewalk, grass, wood chips, and rocks. The rocks picture was manipulated in Photoshop to be a continuous pattern. That's what the line 'Hey Deric and Geoff--nice rocks!' means in the 7.5.3 secret about box.
The pattern that looks like a tannish lattice or tile is actually a picture of a moldy shower in one of the engineer's home. The black on with roses is the skirt of one of the project managers, and the new Scottish tartan colors are the actual ancestral colors of two of the engineers on the update team. One of them is the Dave referred to in the 'Hey Dave, what's under the kilt?' line in the secret about box. Bet you didn't think so much could be hidden in plain sight!"
Ô£øThe Source:
I was probing through the "System" file (version 7.5.2) on a PCI Mac recently and found where the guts of the iguana egg lie. Most of the information for the egg is located in the 'timd' resource, in ID 25. If you open it up, all you see are some typical codes, but close to the end of the garbled test is a line that says "rob's window". It is believed there
is no way to trigger this message in the easter egg.  
ID 31 of the 'timd' resource in "System 7.5.2 Update" file
has most (if not all) of the information in the above ID 25.
On top of that, ID's 26 & 27 have pictures of the Iguana and
the Apple campus respectively. The fix is in there due to the
new Drag Manager in System 7.5.3 which would have otherwise eliminated the egg. The pictures need to be viewed with a JPEG or JIFF viewer. CanOpener did all of it for me. While they were fixing the code for the Drag Manager, the about box was updated to credit people who worked on the system update, unfortunately taking out everyone who worked on it before the update.
Ô£øSecret ROM Image
On a PCI PowerMac (desktop computer only) type "secret ROM image" in any text application (i.e. Stickies), select it, and drag it to the desktop. A giant picture will appear of many Apple programers and engineers. These are the pictures of the people who worked on the hardware and low-level drivers for PowerSurge (the code name for the PCI PowerMacs). Go to my web site to see the picture.
Its primary location (besides the image which is in the ROM) of the trigger is in your System file (7.5.2 or 7.5.3) in the 'timd' resource at ID 30. There is a closing statement at the end saying "secrets lurk in ROM". This resource is the trigger, but the picture lies in the ROM. There also appears to be a fix in ID 30 of the 'timd' resource of "System 7.5.2 Update" due to the new Drag Manager in System 7.5.3.
The secret ROM image cannot be triggered in System 8.
