Found any workaround for this yet ?
I too get screen-troubles with Age of Empires II after upgrading VMWare Fusion because of upgrading to Mountain Lion.
I start multiplayer->create game, and after some seconds it just "booof" and I see the desktop in 8 bit-color with a black square up in the left corner.Have to Ctrl-alt-delete to task manager to be able to do anything.
Tried both full-screen, single-screen and different screen-resolutions. Also tried to disable 3D-acceleration in the VM-settings.
Used to work fine before the upgrade.... 
Im running Win XP SP3 in Fusion 5.0.2 on a Mini Mac w/Mountain Lion.
- Roy