QuickTime 7.6 should be able to convert the MJPEG to MPEG-4 all by itself. MPEG-2 would require something like iDVD or the separately-purchased Apple MPEG-2 components. There's always the various Aquafied ffmpegs, of course, but I've never used them myself.

EDIT: In fact, I just tested it on my Tiger system with some old video I captured from my Fuse card, and it plays and converts no problem (QT 7.6.4).