Don't know where my links went in a previous post, but search the goog for software to do this. I personally use iSkysoft iMedia converter on my mac and it works a real treat. Easily understood and never fails to convert to my chosen format with custom settings abound.
taken from web: What affects the quality is the codecs used. Both MP4 and MOV usually contain the MPEG-4 codecs, which includes AAC and H.264. Other codecs include Xvid and DivX but they're rarely found in anything other than AVI containers.
In terms of quality you should find that H.264 is the best for overall file size and visual clarity. You need a more powerful computer than the others however. Any modern Mac within the last 2-3 years can play SD H.264 videos just fine.