Ned22, it is more than likely Vista as Vista consumes an enormous amout of resources. Where 1GB of RAM was more than enough to run the game under XP, you need 2GB of RAM in your computer or you will be swapping with Vista.
Also cheak the sticky in this forum concerning performance hints and tips with Vista.
However, if you have an onboard video chip, then you probably are going to be plagued by uneven gameplay. Vista is just requires too many resources.
