We've always had open source WinAmp. There are two. Audacious and XMMS. Both available in Linux
If I remember right though, those will run the classic skins, but not modern ones. I got it running okay-ish using Wine, but I could never get the visualizations running.
Probably. I liked Amarok better back in those days, so didn't use XMMS or Audacious much.