what else could I do?

If you have a Unix machine running a samba (Windows file sharing) server, put a file in his home directory called C:\*.*

If he tries to delete that file from Explorer, it'll delete the real C:\*.* (at least on Win95/98. It doesn't work on NT/2K)

If he has a Unix shell account that he doesn't really know how to use, put a file in his home directory called "-rf .*" (with the space) and watch as he types "rm -rf .*" (that one from news:alt.tech-support.recovery)

Peter