Jay--
I had a quick look at the Rhino site, and that combined with the email you posted makes me confident that Rhino is a MusicNet frontend. Musicnet is the DRM provider for Napster, Yahoo, Performer, and many others (but not itunes). So here is my suggestion:
Either give up entirely, and call it a cheap lesson learned re/DRM, or open a free 7-day trial subscription to Napster. I suggest this because the Napster service has macros to go get the codecs or voodoo that subscribers' machines may be missing. When I ran Win2k (I run XP now), you could hear the Napster customer service rep's eyes rolling, as if to say "Oh no, not another Win2k." So I think the problem, if it's not a simple case of antivirus preventing some sort of communication, is probably more like Alex B aludes to, a mismatch of win2k with windows media codecs.
Best of luck, Hombre. If it's any consolation, EVERYONE's having trouble with the MSFT DRM. This is the reason why the labels are considering dropping DRM entirely. Post back your results and we'll try to go from there.