The best free flash player for Mac I've found, is Whimpy Flash Player, available at:
Basic, no bells or whistles, but doesn't crash like others I've tried.
To convert flash (.flv) to mp4. I use isquint, available for free at:
It's mainly for converting video for ipod, but there are settings that let you save the vid in a larger screen format. So far, I've found no clitches.