Yeah, but Winamp comes with the mp3 plugin in the first place, so that hardly counts as a seperate thing to fetch and install

As far as I know, all recent Windows installation include full mp3 decoding support too. Maybe you're getting mixed up with AAC or another format? Even then though, I'm sure if you can get a plugin for Winamp, you can also get a DirectShow based plugin so MS players (or any DirectShow based player) can also play it.
Not sure what you're getting at saying the quality of the AACs were better, but had static so you didn't like them. Seems like a contradiction to me
