I had a similar problem had to do with the Admin Password and I followed these instructions and it worked.
Follow these instructions and after step 5
Go to control panel and do what you need to do from there.
From Computing.net forum, Response #3 (method2) -
http://www.computing.net/windowsxp/wwwboard/forum/157929.htmlInstructions Here:
Lost password, Change Password or Delete Password on XP User Accounts with Admin or limited Privileges.
This procedure only works if you can enter safe mode thru the hidden Admin Account
1-Boot to Safe Mode by tapping the F8 key while booting
2-Choose safe mode, Press Enter
3-Select operating system, Press Enter
4-Click Administrator Account
5-Windows is running in Safe Mode, Click YES
6-At the Safe Mode Desktop, click, Start, Control Panel
7-Double click User Accounts, Here you can delete accounts, delete/change passwords ETC.
8-When done Close all Windows
9-Restart Computer