This thread looks pretty dead, but I'll post here in case someone is searching this site for winamp stuff. There's even more old versions of winamp available at
http://www.winampheaven.net/
Winamp5 has just been released (as of this post) I just tried it and I'm not impressed. Winamp has yet to get video right, at least on my system. There's a plug called vid4wa that works great, I'm using it with v2.81. After reading this thread I'm thinking I'll retrograde to an even older version. Another trick is to steal the stock plugins from a newer Winamp and overwrite the older ones, thus upgrading your sound quality without getting all the other junk they've added. Keep backups of everything, of course.