This is something i knew for quite a while, but didnt think about sharing it, but since it's spreading like spam across the web, thought i'd share it with you guys...All you need is access to command prompt, and you can do it.. here's how it's done:
open command prompt (Start - Run - Cmd) , enter this:
_at minute+1 /interactive "cmd.exe" (ya3ne if the time is 1:20pm , u put **at 13:21 /interactive "cmd.exe"**)
when the scheduled cmd opens, notice how the old one is c:\documents and settings\YOUR USERNAME while the new one is SYSTEM.
go to your task manager (alt ctrl del) and kill explorer.exe's process, then close the old cmd, and from the SYSTEM one, type explorer.exe, which will reopen the explorer but NOT through ur user, through SYSTEM user.. which is like.. root for windows, when the desktop is ready, u're god on that computer
u can edit admin users or create new ones or do whatever you want..
PS: most of the times this doesnt work on guest users, but it worked on some guest users on some pcs..