I can't play any mkv or h264. My comp isn't the greatest, so does anybody know of a good mkv/h264 player or converter for Mac? vlc skips a lot and mplayer sucks.

Well, the first, most obvious, suggestion I can make is to check this thread here to see if that can solve your problem.

Next, I suggest trashing your mac and getting a PC, considering that the real world runs on PC's or Sun/Linux systems. Mac's are only good for 2 things: anything related to graphic arts (i.e. making movies/music, ect.) and relieving stress by smashing the hell out of them. Most top-of-the-line macs that I've ever used are just glorified paper weights with a computer screen so trash your crap-mac and get a PC.

Anyway, now that I've gotten the being rude out of the way, the above mentioned thread should give you a few options. If none of those work, check to see if your player has an update that might make it work properly.