I'm currently trying to complete the Starbase 24 mission where you fight off the Klingons (by the way the text in the game says you're going to Starbase 13). It is common for the game to stutter for a bit then the screen goes gray, then it crashes me to windows. I also have an ATI card, Radeon 5870.
Same for me. I have tried 2 ground missions now, and it always ends with a decompression error, always at the same occasions: during the loading screen of Kassae IV, and down on Regulus helping Paris on the small path when closing in on charge #4.
I have done a file check multiple times now, and I haven't had any problems with my 1st char a few days earlier.
W7/64 (still the prelease version) and ATI X1900
Edit: ok, don't ask why because I don't know, but all of a sudden, my ground missions are working again.
I was constantly crashing when on ground battles... but two options i changed, and now the crashes are nowhere near as often. Firstly, i reduced the terrain detail distance to minimum, and secondly, in the troubleshooting area, i turned it to basic character animations. These or one of these options seem to have cleared up the crashes.