Alright, try this if any of that did not help...
(At home) Make a DOS boot disk, download NTFSDOS (which is a program that allows DOS to read an NTFS partition) and put it on the floppy.
(At school) Pop that baby in the system, boot from the floppy, run the NTFSDOS program, copy the SAM file to the floppy, remove the floppy, and return home.
(At home) Download @Stake L0pht crack program (http://www.atstake.com/products/lc/
) and run it against the SAM file you stole.
If you want more help in this you can email me, or respond to this post.
I have done this at my school (When I was in school). It really depends how the network is setup, most schools use Active Directory (Domain Structure) so you can only get the local machines admin password (In most cases it is the same as the network administators password.) The network administrators password is stored on the domain controller.