I just used this tool to reset a Vista password - it is a Linux boot CD very simple and effective. So if you've forgotten your Windows XP or VISTA password, don't despair - this tool will get you back in business FAST.
See: http://home.eunet.no/pnordahl/ntpasswd/bootdisk.html
A very good walk-through is provided here:
http://pcsupport.about.com/od/toolsofthetrade/ss/ontpre-screenshot-guid…
Oh, and yes, it's completely FREE.