These torrents included all the tracks that could be previewed on the SXSW website for SXSW 2012. This year's collection included 1,219 files totaling 7.52GB. Note that the filenames and ID3 tags were updated to properly reflect the artist names and song titles.
The first torrent was seeded February 16, 2012 and the second on March 7, 2012.
If you need a good BitTorrent client, I suggest:
Disclaimer: This site is in no way affiliated with SXSW or any SXSW artists. These torrents are provided as an alternate means to sample the songs available on the official SXSW site.