Yea, I finally got sick of seeing WMP Not Responding and 70%+ of my quad core in use for ever, every time I started up WMP. I had already modified the library settings to NOT include MyPictures or MyMusic, but WMP blithely ignored that and went on to scan, index, and preview my 20,000+ pictures every time.
Finally fixed it by going to c:/users/username/appdata/local/microsoft/mediaplayer and simply deleting ALL of the Windows Media Library files (after first making sure my libarary definitions were the way I wanted them to be).
Make sure you stop the media sharing service first, or you can't delete the files. Sounds drastic, but it worked. Seems like there's a glitch in how WMP "forgets" about previous library databases. Sigh. Anyway, now WMP starts relatively quickly, and only consumes all of my cores for about 5 seconds.