1.)  Download the appropriate pre-patched UXTHEME.DLL file:  XP-NON-SP1 or XP-SP1 to a temporary location on your hard disk and unzip it. 
2.)  Boot your computer with an MS-DOS boot disk or into safemode if you have ntfs.
3.)  Navigate to C:/Windows/System32 and backup your existing copy of UXTHEME.DLL by renaming it to UXTHEME.OLD.
4.)  Copy the new UXTHEME.DLL file that you unzipped to C:\Windows\System32 and C:\Windows\System32\Dllcache.  If you are installing the SP1 patch, also copy it to the C:\i386 folder or to the C:\Windows\ServicePackFiles\i386 folder, whichever you may find on your system.