I'd just install Irfanview and the related plug-ins for it, and call it a
day. Irfanview (freeware for home use) plays just about everything except
for certain .avi files, .asf/.asx (even those it will sometimes play) and
.ram files. FYI: I also very rarely use WMP9 (resource hog) and
RealALTERNATIVEPlayer, which is just a little buggy, but it is ok. Certainly
not as big a registry glutton and "nosyware" as is RealPlayer.

Anyway, on the tools>options>privacy tab of WMP>uncheck the "I want to help
MS software and services blah-blah". I'd also go through every tab in the
options (particularly privacy and security) and uncheck everything in there.
MS WMP9 is also too nosy for my liking. You cannot disable (unfortunately)
the check for updates feature. I set that for once a month (the longest lag
possible) Some features will need to be enabled, but the bulk of it can be
disabled IMO.

Irfanview
http://www.irfanview.com/
What is it? A viewer, a (simple but decent) photo editor, plays video, mp3s,
ra, rm, some .avi files, and far too many other things to enumerate. Even if
you didn't want to use it for Mp3's (unlikely) you'd find it to be a great
program for most other reasons and purposes.

HTH -

If you haven't seen it yet, here is what IrfanView will do/play:
http://www.irfanview.com/main_formats.htm