Recently I was trying to log on to a PC(recent gift) that had Windows XP Home Edition that had password protected accounts. I was a bit baffled at first but after some research I found a relatively easy work around.
First you reboot the computer and log onto "Safe Mode" (usually by pressing F8 but some PC's differ). This will log you on as an "Administrator". Go to "Control Panel" then "User Accounts". From that point you can change or add/remove any password on any account. This could be a great way to to play a joke on a loved one/friend too (but you didn't get that from me of course). This only works in Windows XP Home Edition and not XP Professional which has tighter security. With XP Pro you'd probably need some third party software to crack the password like Ophcrack or something similar. I've not tried this so I can't vouch for it. Good luck and have a great day.