Doing a quick google search using "mt4 on mac" yields many conversations on using MT4 in a Mac environment.
Our own personal experience is with testing demo MT4 using the Parallels program to run Windows 7 on Mac OS X. MT4 seems to work fine in that environment. Of course, to run Mac OS X and Windows together, you probably need much more than 4 gigs of RAM for it to run smoothly, especially if you're running multiple programs at one time. Hopefully that helps you get closer to an answer.