Please make sure that you have the latest video card drivers from the manufacturer's website, particularly if you have an NVidia card. You'll get the Alt-Tab crashes a lot more frequently if you don't have NVidia's newest drivers. Nvidia's website is http://nvidia.com and for ATI cards, http://ati.amd.com
Also, if you increase your resolution to match your monitor's resolution and uncheck the Fullscreen option, you'll run in a fullscreen window which will give you faster alt-tabs without crashes.
If you are still getting crashes and are on XP, please install SmartException from https://www.stardock.com/products/smartexception. Also, if you have a save game that reproduces a problem that you report, please zip the save game and attach it also. If the problem you are seeing is graphical in nature or a screenshot may help explain the problem, please take a screenshot by hitting ALT+Printscreen and then paste into MS Paint or another paint program and save the image as a jpg.
If SmartException does not pop up a dialog, you can manually generate the exception log to send in to us. Right click on the SmartException icon, select a crash, choose E-mail selected exception. Fill in the text box under How to reproduce this problem, then click Generate exception. This should cause a folder to open (Default location is C:\Program Files\Stardock\SmartException\ZippedExceptions) containing a file ExceptionLog.zip and mailinfo.txt. Sometimes interference from Anti-virus or security programs may cause the zip operation to fail, but the files will still be there and you can zip them yourself.
If you need a response from a support tech (eg the game crashes when starting up, starting a new game, or loading a save game) e-mail the files to support@stardock.com. Otherwise, you can e-mail the files to gc2bugs@stardock.com which will save the support techs the time of having to forward it to the developers. In general, if it's a consistent crash, send it to support@stardock.com. If it's a random or unreproducible crash and you can continue playing from a save game, e-mail it to gc2bugs@stardock.com
SmartException doesn't work on Vista yet, but if you are getting a consistent crash, please zip up your save game and send it in to support@stardock.com with your debug.err file from My Documents\My Games\GC2TwilightArnor and a description of what was happening at the time of the crash.