I am having the same issues as AlphaD...sort of.
Installed MM and played a freeform game with old unlock hack to see what was different from the Beta and not a problem computer wise. (no other usermade downloads).
Installed new mm hack and played freeform...no worries.
Decided to play a challenge game and bang! freezing screen and an error message that my graphics thing stopped responding. Comp put itself in safe mode and i quit.
Dumped temp files, cleaned up disk, defraged ect ect then updated graphic card drivers (radeon 9250) and I can play free form ok'ish, just a bit of lag, but if i try and play the challenge games..... i am lucky 'if' i get 20 minutes play time before a frozen screen and having to restart computer.
Will reinstall, and see what happens.
Edit to add:
Reinstalled all but DD and no hacks. Played a campain in each as i installed and all was good until MM was installed. Thats when the freezing began. Lowered the scale for direct draw in computer settings and I got to play 2 full senarios in campain mode before freezing. Was a bit annoying with the cursor fading but at least I got to play.