Hi Stacie!
That last Baldur's Gate compilation we published was put out before Windows Vista. We never published a version that required Vista and we're not the publisher of the Baldur's Gate series anymore. Is it possible this is a new release from Atari?
In any case, I can't imagine why it would require Vista and not work on XP.
Sorry that we can't be of more service. I'm personally very intrigued by this. Would it be possible for you to scan the box cover (front/back) and maybe the DVD label to post here? That might give us some more info to go on.
Here's a link for Bioware's great support site for Baldur's Gate:
http://www.bioware.com/games/baldurs_gate/support/
pax,
-Chris