If you bought Windows XP and have been unlucky enough to fail the validation (which isn't uncommon) then you might just want to remove the Windows Genuine Advantage (WGA). This is a non-vital Windows component, which means that without it your copy of Windows XP will continue to work.
If you have tried to delete WgaTray.exe and it says "Access is denied" then 1. Launch Windows Task Manager. 2. End wgatray.exe process in Task Manager and retry. if it doesn't work then 3. Restart Windows XP in Safe Mode. 4. Delete WgaTray.exe from C:\Windows\System32.