I'd just sit 'em down and talk it out. They should have respect for you as their roomate at least, seeing as you are not directly involved in whatever the problem is. You are right to say that you are caught in the middle, and that's not very fair. If they can't settle their differences and grow up, I'd look for new roomates. Also, the easiest option is to boot out the person who instigated an act of phsyical violence first.
Thanks for the advice Circus and Jack! I think a talking it out is the best thing to do, but I have to wait a while for their tempers to cool off. Otherwise a discussion will degrade into an arguement/fistfight. Also since i wasn't around for the fight I can't determine who started what, since each blames the other one. If I knew who it was I would make him leave! Finally I'm trying to avoid the hassle fo getting new roomates, since I only have so long until the college year is over, however I definatly ain't rooming with them again!