Here is something that I got today from bah4ever forum by user shine.
Have you forgotten your password and you don't want to re-format your
computer ? Well here's what you do.. Please note that this only works
on Windows XP !
PLEASE READ CAREFULLY !
1. Restart you computer
2.When booting, press F8 and select "Safe Mode"
3.After getting to the user menu. Click on a user and this time it
will not ask you for a password
4.Go to Start>Run and type "CMD" (without the quotes).
5.At command prompt type in "cd C:\Windows\System32" (without the
quotes), I am assuming C is your System/Windows Drive
6.For safety purposes first make a backup of your Logon.Scr file.. You
can do this by typing in "Copy to Logon.scr to Logon.bak" (without the
quotes)
7.Then type "copy CMD.EXE Logon.scr"(without the quotes)
8.Then type this command, I will assume that you want to set
Administrator's password to "MyNewPass" (without the quotes)
9.Now, type this in (I am assuming that you are still in the directory
C:\Windows\System32) , "net user administrator MyNewPass" without the
quotes
10. You will get a message saying that it was successful, this means
Administrator's new password is "MyNewPass" (without the quotes)
11. Restart the PC and you will login as Administrator (or whatever
you chose to reset) with your chosen password and Enjoy!