Enhanced Maintenance script

I’m reposting this question since my previous might of been rather vague. The script I have is very simple and runs as a logout hook without any problems.

tell application “Finder”
move (items of the desktop whose kind is not “Volume”) to trash
end tell

The only issue is figuring out how to have this hook enabled for one user only (student) and more so empty the trash when reaching a certain level (over 50MB).

Any suggestions??

Model: MacBook
AppleScript: 2.1.1 (81)
Browser: Firefox
Operating System: Mac OS X (10.4)

Scratch that. Figured it out through a few UNIX shell commands. If anyone needs the code hit me up.