Banscare

Enter the BIOS and change the boot order to boot from CD. Boot up with the OS CD in the drive, Install your OS. You are now the administrator. There may be a BIOS password set depending on the school's policy but if thats the case carefully open the laptop (consult documentation) and pull the silver flat battery out for a few minutes. This flashes the BIOS erasing any passwords. Buying a new hard drive will also work.

*Laptops can be a pain to disassemble so take your time.