ONTPRE does the job

Offline NT Password & Registry Editor [ONTPRE] is what you need. The download can be found here:

http://home.eunet.no/pnordahl/ntpasswd/

There are step-by-step instructions here:

http://pcsupport.about.com/od/toolsofthetrade/ss/ontpre-screenshot-guide.htm

This program will delete your password(s), so you can gain access to your computer again without losing anything. Works on W2K, XP & Vista OSs. Best of all, it's free! Good luck.