The steps in this article were figured out with Windows 7. However, they should work just fine with Vista for anybody having the same issues. Note that whilst this is written for ATI hardware, it may be the case that NVidia gear suffers from the same problem and this solution should help.
Background first. I spent a while sorting our AV gear so I could use HDMI as the universal connection standard. At the heart of this is an AV receiver with a number of HDMI inputs and HDMI output to the TV.