Two choices that I know of: Buy the MPEG2 QuickTime component from Apple ($20) and then use QuickTime Pro (if you have it--another $30 if you don't) or any of the wide variety of Quicktime-based transcoding tools available through a search on VersionTracker.
Alternately, you can get your hands on a program that can transcode directly from MPEG2 (SVCD) to another format, and use that. FFMPEG is wonderful shareware that'll go from just about anything to just about anything, and there are likely others. Again, VersionTracker is your friend.