I too have had difficulty making this plugin work. I was initially using V. 5.6 of Winamp on WinXP, which is apparently incompatible. I just downloaded and installed V5.0 and it also doesn't work, so I'm about to try V3 and see if that works any better.
--No, V3.0 of Winamp also does not work in game. I remember long ago when B&W first came out I did get this plugin to work, so it's odd that it won't now.
I'm not too worried about getting this plugin to work though, I guess I'm just confirming that for whatever reason it doesn't like me =)