Maybe this post can be helpful. Perhaps not the easiest solution..
www.wargame.ch/board/acw/topic.asp?TOPIC_ID=12850
EDIT: Looks like the forum is down. Here's the post:
"I am currently successfully running all Battlegrounds titles both ACW (except Chickamauga)and Nap titles on Vista.
How? I installed them onto my laptop (Windows XP), updated them and then COPIED them to a flashdrive then to my new Vista computer (not to program files but to a new folder, Games/Battlegrounds/"game title"--Nap titles PTW & BGW must be installed in the root directory of whatever drive you choose). Right click on the start icon, create a new shortcut and they 'seem' to run fine. I do use a master disc.
NB: I have not yet played around with Chickamauga nor have I approached this problem from a scientific inquiry with screwing around with all the variables. I just tried this and it worked, so I thought I'd pass on the idea.
Capt. Neal Carney"