The Washington Post (by way of PC World magazine) has a little article on how to take a picture of your TV screen. The main thing is use shutter priority mode, and a speed of about 1/20 of so. Also, tory to shoot with the lights out or in an otherwise darkened room.
If you have a plasma, it's a little different because of the way the picture is painted on the screen. You can pretty much do anything and get a decent shot.
