There is a tool out there that is Linux based that will let you hack the SAM database in Windows and change the Admin password without having to know it. It's Linux-based (ironically) and there is an ISO of it that you can build a bootable CD with it to use. Currently, I can't get to this site because my work place blocks such stuff, but I think you might find it here
I've used the tool before, and it works great. I hope this helps.