We sort of did that to our school computers by removing the BIOS-battery and keeping it out for at least 30minutes. Next we ran a program called OPHCrack (can be downloaded from here:http://ophcrack.sourceforge.net/) and mounted it to a DVD, using Nero Burning Room. Later we booted the computer from the DVD and extracted the admin password (OPHCrack is quite self-explaining). There is offcourse not necesarry to have the admin pswd to instala new OS as this can be done from the bootscreen, either with a HDD, CD or USB. So currently i'm running both XP and Windows 7 RC on my school computer and it runs like a dream! Hope this was an answer to your question!