Bah, best prank ever is always the same.
1. Go to sales, dev or gfx design office
2. Find unlocked Apple or Windows PC. Unlock if you are the sysadmin.
3. Open web browser.
4. Go to windows93.net
5. Press F11 for fullscreen.
6. Get to the nearest coffee machine and grab some.
7. Go back to sales/dev/gfx dept. and listen to poor sales/dev/gfx person panic.
EDIT: I just realized I suggested same thing on this same article two years ago xD