Mac Geekery has a cool guide to making your laptop (in this case a Mac) delete your important files in the event that it gets stolen. The meat of the thing is a shell script that periodically checks a remote web server for a file called "youve_been_stolen," and if it finds the file it quietly deletes the files in your home directory. You can also make it alert the new owner that it's stolen and any other shenanigans you can think up. This method could be extended pretty easily to Windows, but you'll have to figure it out yourself. Just make sure you've got your important files backed up somewhere, 'cause even if you get your laptop back you won't be getting the files back.