XP Pro Administrator log-in

Try booting up in safe mode. You can access the Administrator account from there. Note: I said "Administrator", not "Admin".

To boot into safe mode, while the computer is starting, when you see the black screen and before it says "Windows is starting", press the F8 key at just the right moment. You will be presented with a menu to select Safe Mode from. If you don't get it the first time, let it boot, shut down normally and try again.

See this website, I think it has the answer you want.

http://windowsxp.mvps.org/admins.htm

Try these Steps :
-Download Hiren's boot CD
www.9down.com/Hiren-s-BootCD-v7-8-6150/
or
http://www.password-changer.com/download.htm

-Boot From this CD then choose Active password changer.
- let it search for SAM
- Choose the Administrator Account to make his password is Blank .
- Reboot your System .

Press CTRL + ALT + DEL twice at the Welcome
Screen (For Xp Pro) and input your
Administrator password in the classic logon
window that appears!

To have the Administrator account displayed
in the Welcome Screen:

Download TweakUI from here:

http://download.microsoft.com/download/f/c/a/
fca6767b-9ed9-45a6-b352-
839afb2a2679/TweakUiPowertoySetup.exe

Open TweakUI and click!

"Logon" option in the left pane. Put a
checkmark against the option "Show
Administrator on Welcome Screen". Click OK to
close TweakUI. Logoff and see if Welcome
Screen lists Administrator login. Changes are
immediate and you can use the Winkey + L to
switch back to Welcome Screen to see
Administrator account is listed.

Use this procedure to hide/unhide any user
account from the Welcome Screen. Please
remember, you can still login to a hidden
account using CTRL+ALT+DEL classic logon
method, but cannot Fast User Switch to a
hidden user account.