Here is how can you login to your Windows xp computers without any password?
Just make a bootable CD/Floppy.You can easily create it with Nero or a floppy with format command.
boot your pc with it,type the following(assuming your windows is in C: drive):
ren sam sam1
cd c:windows epair
copy sam c:windowssystem32configsam
plz plz comment
If you find any problem plz ask me.I will help you.