I've only seen SPCs in ZIP files very very rarely. However, where I usually go for SPCs (99.999% of the time) is
http://www.snesmusic.org Hopefully that answers your question.
As for playing SPCs in Winamp using SNESAmp, all you have to do is rename them from *.rar to *.rsn (which has already been said). If you downloaded them from snesmusic.org, then they're already named that. Of course, you can also use DrO's in_zip, but I much prefer the way SNESAmp reads the file over the way in_zip does it. On top of that, playing the SPCs from RSN, as opposed to RAR, allows you to view the tag data anytime you want, with out playing the song. Whereas in_zip does not yet have that support in it yet.
Hopefully all concerns have been cleared up. Good luck getting those SPCs playing, and be sure to check snesmusic.org, as I'm sure they have plenty to choose from. Mouser X over and out.
