Create Screensaver
Picasa maintains a separate folder for files used in your screensaver. When the Picasa Screensaver is chosen in Windows, your pictures will be shown whenever your computer is idle.
To add pictures to the screensaver:
Choose some pictures
Choose Create->Screensaver from the menubar
Your files will be exported with all edits and added to the screensaver folder
To remove files from the screensaver:
Search for the name "screensaver" using Picasa's search field.
Delete the files you wish to remove.
Hit ESC key to clear your search
To disable the Picasa screensaver:
Choose "Display Settings" from your computer's control panel
Choose the "Screen Saver" tab
Choose a new screen saver, or (None) if you do not want one.
Click OK to save settings.