Apple TV/FM Radio System - Manual (Page 10)

3 Installing the Card and Software
Important The TV portion of your TV/FM tuner card will
not work if you do not have a video input card already
installed. To see if your computer has a video input card
installed, check the back of your computer for these three
protruding ports.
You need a video input card even if you do not intend to
connect any video equipment (such as a VCR or video
camera) to it. If you do not have a video input card, purchase
it separately from an Apple-authorized dealer and install it
according to the instructions that come with it. If you have a
video input card installed, go on to the next section.
The steps for attaching the TV/FM tuner card to your
computer vary slightly depending on whether or not your
computer has a built-in monitor.
If these ports are present, then a video input card is installed.