It could be the video card but I think that your RAM might be overloaded.
I had the same problem playing StarFleet Command. After 2 missions the computer would freeze. When I upgraded my RAM to 64 MB (from 32MB) the problem was solved. But without upgrading (Although you should get a new video card) you can make sure to save the game often, and close any programs that sit in the Virtual Memory and RAM such as virus scanners, messaging sytems (ICQ, AIM, etc...), download monitors (getright, gozilla, etc...), although these programs aren't running, they are sitting in system memory and this could be causing your game to freeze.
Hope this helps.
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"I'm too out of shape for a long fight so I'll have to kill you fast"
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