Even at this time, people still ask how to play MOHAA on a MAC. Here is a little tutorial that allows you to play on MAC OS x.
Download & Install Portingkit
Download and install Portingkit on your MAC. Register an account and login.
Get MOHAA on your MAC
You will need to get the Windows version on your MAC. I tested it with the Revival edition. You can extract all files from the Revival executable with the Unarchiver app:
Running the game
When all files are extracted, you can right click on the executable that you want to play and select: "Open With" -> "Porting Kit.app"
Porting Kit will now ask to port the game, select "Medal Of Honor Allied Assault: and press "Ok"
Your game should now start on your MAC!
Note: This doesn't support AlphaMAC anti cheat since it does not support MAC at this moment.