Sorry but Intel doesn't have drivers available at their site for that controller. I know as a fact Intel 845G will not support Vista's Aero theme or any of the nice features since it is not a Directx 9 capable graphics chip. I'm afraid you'll need to buy a new video card. Is this computer we are talking about a Laptop?
If you just want to get a decent Vista basic theme display you can install the drivers by going into Device Manager and manually selecting the driver you will be installing. If you believe you need some help doing this, please feel free to ask
