Also if you have XP home, you can press F8 right before Windows loads and select the option to boot into safe mode. It'll automatically log you in. Then, like normal, go into the control panel where you can edit/delete passwords with complete Administrator privileges.
(Note: The account that logs in when you are in safe mode is the Administrator account on every XP computer. With XP Pro, though, you can log in uwing Quick69GTO's method, but that method is disabled on XP Home)
If that doesn't work, you can always get the ophcrack linux live cd
http://ophcrack.sourceforge.net/ and boot up to crack your windows password.
Good Luck