I have tested the game on Mac OsX 10.6.3 with Cross Over Games 9.0 For Mac. If you try to run the game in full screen, the screen view is not complete (i.e., you see only a portion of the game). However this can be overcome by emulating a virtual desktop and running the game within it.
Might and Magic 6's native resolution is 640x480. Thus, you might want to set your desktop to that value. After that the game might seen tiny, so you might also want to change your desktop resolution to a lower value (still larger than 640x480) to see the most of the game.
To emulate a virtual desktop.
Click configure -> manage bottles
Select the bottle that MM6 is installed
Go control panel and start wine configuration
Go graphics tab, check emulate virtual desktop
For desktop size enter 640, 480
and you are all set!
I am using the win98 bottle. I haven't played a lot by for the beginning the game installs and works flawless.