Windows Vista has some problems running current games, so imagine "how well" it can run old MS-DOS titles (tip: forget about it ;)
The other day, remembering old games I didn't finished and I sould have, I remembered that I've played Ultima VIII far more than Ultima VII (yeah, I'm ashamed), so I searched for a solution to install it on my laptop (which runs Windows Vista now).
After some work, I found Exult, a marvelous open-source engine that runs both Ultima VII: The Black Gate and it's expansion Ultima VII: Part Two - Serpent Isle.
Apart from some tweaks, cheat modes/debug modes, new options and a few bug fixes, the most important feature is that it allows to run the game windowed and in almost every resolution.
So, if you wanna save Britannia as the Avatar in one of the best RPGs out there, give this a try ;)