The most excellent Rafael Rivera who originally modified the uxtheme.dll file in XP to allow it to load un-signed themes and visual styles has a repository of pre-patched uxtheme.dll files for all versions of Windows.

If VistaGlazz doesn't work for you, or you are using Vista SP1 or a 64bit version, head over to Within Windows and grab a pre-patched uxtheme.dll file your your system.

It's a long list so be sure to grab the correct version for your system. If multiple version are listed for your version of Windows, just open System Information in Windows to confirm your exact version (look for 'Hardware Abstraction Layer', for example, XP SP3: 5.1.2600.5512).