SXSW Baby is a good source of every arm of the SXSW festival (film, interactive, music). Each year, Kathryn Yu updates her excellent FAQ and howto for the music festival.
I. What’s the format?
II. How do I get in?
III. Who’s playing? How do I maximize seeing live music?
IV. How to overextend yourself at SXSW, or, How I Learned to Stop Worrying and Love South By
V: How do I stay on top of SXSW news?
I’d say that 90% of all your questions will be answered in that post so read it before asking those questions on my site. :)