disable streaming video while logged innto HTPC running vista & ultraVNC

I just rebuilt my media center PC using vista 64 ultimate (it was XP pro). i switched to ultraVNC because it works with vista as opposed to using tightVNC in the past. however, whenever I watch an HD movie at full screen, i have to close the viewer because it makes the plasma monitor choppy. Once closed, it's smooth as butter. i'm assuming this is because of network issues when the viewer is open. The viewer will attempt to display the video (choppy with lag). i've tried turning down the colors, but it still displays with less colors. So.. i haven't found an obvious way to simply disable the streaming video to the viewer session. With tightvnc, it would never show the video at all, so i've never had to deal with this before.

Any suggestions?

Thanks!

I don't believe I have it running, as the server shows the "video hook driver' unchecked , unless I'm missing something else somewhere..