If you have the Logitech G15 keyboard, theres a nice little plugin to display Teamspeak info on the LCD, it shows the people talking as well as joins and departs.
http://www.schmads.com/g15tsdownframe.html
oh nice, ill need to get this when i get home
If you dont have the G15 keyboard, this supposedly works in game
http://www.wowinterface.com/downloads/info10012-TeamSqueak.html
If that doesnt work for you, here is another application.
http://www.voice-overlay.info.ms/