Update August 2007: If you are having memory issues on Vista, please read this Microsoft knowledgebase article:
Update: June 2007: Version 1.6 of Galactic Civilizations II: Dark Avatar should have no problems at all on Vista at this point as long as your NVidia video card drivers are version 158.24 or higher.
If you have a laptop card, check the support section of your laptop manufacturer's website (Dell, hp, etc) for updated drivers. If the driver version is not 158.24 or higher, you should contact your laptop manufacturer and ask them when updated drivers will be available. The more of you who contact them, the more incentive they have to update their drivers. Otherwise, your only other option is to use the modified drivers from a third party site like LaptopVideo2Go, but this may void your laptop warranty so check the terms and conditions of your warranty first.
Update Mar 3 07: The 101.41 beta drivers appear to contain the fix for the issues discussed in this thread. If you are using an nVidia card with Vista, check nVidia's site for these drivers (or newer).
If you have a laptop and the manufacturer does not provide new enough drivers, try the ones here.
Update May 7 07: Version 1.6 beta 2 for Dark Avatar resolves the scrolling slowdown issue.
There is a known issue with GalCiv2 and Dark Avatar on Windows Vista and an NVidia video card. With the older version of the drivers, this could manifest as a crash or hang, or sometimes a hard lock. With the latest drivers for Vista, the game just stops repainting but can be shut down by hitting ALT+F4. It is typical of this error to see the message "Error flipping back buffer" in your debug.err file.
We are working with NVidia to resolve this issue. It may help if we send in the system information for additional systems, so if you encounter this error, please send your debug.err file to email@example.com with the subject line "Vista NVidia error" or something along those lines so that I can quickly identify them and send them to my contact at NVidia. Dark Avatar and GalCiv2 have their own debug.err files, so make sure that you send the one where you got the error. Please only send in the report once.
You may also want to save your last autosave before the error so that you can test to make sure that new drivers have fixed the problem once NVidia has releases a new version, but you don't need to send in the save games at this time.
Currently, there are no known issues with ATI cards on Vista, but you may want to make sure that you have the lastest drivers anyway.
Please make sure that your debug.err file is included with any reports you send in, as SmartException is not currently attaching the debug.err file in its reports for Dark Avatar.
Update: NVidia has identified a problem in their drivers, which will be fixed in their next release.