It was mentioned again last night so I thought I'd repost the information about this.
Teamspeak Overlay (TSO) is a program that allows you to see who is talking in-game.
It can be downloaded from http://www.teamspeakoverlay.com/
You install it and it should create a program icon like any other program. I've found it best to start everything in this order:
When you start TSO it will give you the "This is Beta software......." message. Click 'OK".
Then a dialog box. Select Enable
, then select Hide
Now when you are in-game it will display who is talking and your framerate and the time. It will only display this information while in game.
There are other Options you can change on it's menu.