Reset Snow Leopard user accounts/preference
Name of hard drive
Click enter, rename it
Menu items in Finder
What do you mean by that?
Dock size and items
Trashing ~/Library/Preferences/com.apple.dock.plist will do the trick
Size/appearance of things
Trashing the .plist file under ~/Library/Preferences
Even some applications have been moved from their original location
You'll have to move them back to /Applications manually.


In order for that not to be reproduced, you could try Parental Controls under System Preferences > Account and limit what they can do on their account.