Hussar
Legend
I've used background music and sound effects in my MapTool sessions before. The dripping water effects in the sewers was a hit as was the splashing water when critters came running through the water.
I usually use Ventrilo for voice as it is very lightweight. So I use a second instance of the Vent client on my GM machine which is hooked directly into WinAmp via a virtual audio cable. I have a playlist of background music and sound effects loaded and when I need them, I just double-click and the entire group in Ventrilo hear whatever sounds I play. It worked really well. It does take a little bit of setup.
Heh, that's a bit beyond my capabilities.

Although, I did just see this little gem - Social networking site for synching Youtube videos across multiple users. Very sweet. I could see using that very easily, and it runs in your browser: YouTube Social brought to you by Socialvision - www.socialvisioninc.com