I experienced some problems when running GalCiv2:TA on Windows Vista SP1 (also tested on XP). Runs on a Q6600 with GeForce 8800 GTS and all drivers up to date.
The first thing I tried was to uninstall everything and delete all game folders, then reinstalling. First I have to disable "Hardware T&L" and "Enhanced ship rendering" to have it stable, but I can live with that. Major problems remain:
1) Can't select custom race! The icon for the choice simply does not appear.
2) The game almost always crashes during planetary invasion. I can prob. give a dxdiag printout later.
On XP it's a pretty ok, however I have to kill the GC2TwilightOfTheArnor.exe process manually when the game crashes.