I have a suggestion, though I don't know if it'll be pertinent. Try disabling the "Steam Cloud" functionality. It might be causing a problem because it has to synch your game saves every-time you load a map. I only noticed it happening because my load times were 30 seconds or more when loading a map or the star map.
Running Windows 7 32bit 6850 Radeon 3 gig ram Steam Version of it, Match's trainer version. No AV installed atm. I even try'd it in offline mode and disconnected from the internet. Imperial Guard as my race.