I know that it is possible to clean up a folder with an folder-script. I mean, if someone is putting something into a certain folder, you can automatically transfer it to another place. But can you do the same trick with files who are put onto the desktop??? Can anyone help me with this tricky question???
You can do it easily, two ways:
Folder Action Setup, a control panel: http://www.macscripter.net/tools.html#t10
Attach/Remove Folder Action, a simple script:
Mount my public idisk: idisk.mac.com; user=julifos;password=public (Chooser > AppleShare > Server IP Address); navigate to AppleScript Projects > Attach_Remove_Folder_Action.sit
A little complex 
Perhaps the best way is look yourself to Folder Actions’ dictionary, which is rather simple (located at your extensions folder).