I think Colosseum uses a lot of memory so running something else (i.e media player, recording program) may causes the game to crash.
Unless you got a really strong computer than I think xfire shouldn't have any problem.
Colo's just buggy I think. It apparently caused (maybe still does) problems when it came out in Japan too. Actoz isn't exactly renowned for writing good stable code, remember how big a mess Vintor was? (It kept crashing the server, apparently it did the same thing when it was first released in Korea.) So it's going to be sensitive to pretty much anything you have running, not just xFire.