At startup MacPipes X always runs in a window, showing its suitability for the Mac OS X environment. If you have a screen that supports resolution switching, MacPipes X has an option to resize your screen to 640x480 for a full screen gaming experience (the actual game window size is 512x342).
You can switch to full screen (and back) at any time, even during a game, by selecting the command "Full Screen" from the Game menu (Command-F).
When in full screen mode the menubar is normally hidden and can be revealed by moving the cursor to the top of the screen.