I have a Radeon card with a tv out and I use it all the time. Unlike a dual monitor system it basically mirrors the main monitor. I've got mine connected to a 13" tv/vcr combo to enable taping of any streaming audio or video files. You'll most likely have to do some initial fooling around with the monitor controls as mine totally foobarred the geometry settings of my monitor the first time out
I also have a second monitor, but that's a whole 'nother story. Hopes this helps