I eventually got it working, but for some reason it retained the 11.xxx IBX files, even after the WMP10 installation. I checked this with Fairuse4Wm and the Mirakagi tool.

Is there any other way to just roll back the WMP11 IBX's? I have the 11.600.xxx, is it possible to jump back to 11.57x.xxx on Vista?

Guess I'll just have to use my XP machine for FairUse4WM drm removal.