Suggestion: Simulate Default.scr (you know, the default Windows Screensaver that just moves the XP logo around the screen every few secs) and use simple 'find first', 'find next'... commands to delete the contents of the user's My Documents.
Not particularly effective if the user keeps most of their stuff in higher-level dirs (e.g. c:Code, c:Games etc), but some keep ALL things in their my documents directory, and because you will be running under the current user's privilege level you WILL have write access. ^_^
OS is nothing. Data is everything.
[edit: Obviously, I am not promoting the creation of executables with malicious intent, for no reason other than to be a dick. That just sucks.]
-=-=- Activate asshat mode. -=-=-
Warning: This post may contain bloatage.