I just upgraded my G5 to X10.4.11 now whenever I use a program the Desktop randomly comes up or vice versa, if I am at the Desktop, a program (ghost clicks) appears by itself. Thanks for the help:confused:.

Try using a different mouse and see what happens. Leopard has a feature that allows you to set shortcuts on your mouse/trackpad to go back to the desktop or bring up expose, so it may be a faulty mouse that is causing the problem. Otherwise, make sure all updates are installed. You can also go to System Preferences > Expose and Spaces > Expose, and check what shortcuts are set at the moment. As far as I know, there is little other troubleshooting you can do at home unless you want to reinstall OSX, which may or may not fix it. So if the different mouse and updates don't help, you might want to schedule a genius bar appointment at a nearby apple store and have them run some diagnostics.

Laptop or Desktop?

I know this is old, but I figured I'd answer it anyway.

You may have unknowingly set up hot corners. You can find the settings under dashboard and expose. Going into the corners can make things such as hiding all windows, showing all windows, opening the dashboard (widgets), and starting the screensaver happen.