I would avoid codec packs like the plague. I have never had anything good come from installing those things, and every time I've done it (which admittedly hasn't been for 7-9 years), I've always felt like pieces of it were always on there no matter how hard I tried to uninstall it. I recall one time that I reformatted my computer partly because a codec pack installation screwed everything off and reinstalling Windows was just easier than fixing it.

Switching to VLC for all video playback made life a lot happier. Frankly, Doug, I'd recommend just using another program for audio playback. I wouldn't really recommend VLC for audio, but I'm sure there are some nice alternatives out there. I've never really liked WMP very much, and I'm not surprised it's acting weird.

One thing you could try is installing the Zune software. It's actually really nice for music playback. It has a very attractive interface. It's very much form over function, but it's still as functional as other music software out there (which isn't saying much).