Teamspeak Overlay is an add-on application to teamspeak that allows you to access the controls in-game. You install it seperately to Teamspeak. It's not natively compatible with Vista, but you can run it in compatibility mode (right click on the shortcut icon, the option is in there). However I'm not sure if you can set it to run in 32-bit mode in a 64-bit environment, as I've never used the 64-bit OS. I think I remember reading that someone got it working on Vista64 by doing this though.

Just google for Teamspeak Overlay and you'll find the application easily enough.

I installed TSO but stopped using it as it seemed to adversely affect my in-game FPS (more to do with my rig than the application I'd say).