You might try rebooting your computer, then running the game with many of the features turned off. No music, low graphics, no fade screens, etc. You dont have to change those for ALL your games. It can just be for the one you are having problems with. Some help for that is here...
http://forum.shrapnelgames.com/showthread.php?t=44262
The map can also be a problem if the graphic part of it is too high-resolution. But that is really hard to try and change in mid-game.
Or you might zip up the game (and the map) to send to a server so they can run it for you. I can do that if you want to send it to me. That way you can connect over the net and the server does the heavy processing.