When it comes to HTPC, there are literally 10, 15, even more possible resolutions. Because you're in control of the machine, you need to ensure you're displaying things optimally.
This section applies if your HDTV set has analog high-definition component inputs or high-definition RGBHV inputs rather than digital inputs such as DVI or FireWire. Most HDTV sets don't have a VGA input.
If your set has a digital connection (DVI, HDMI, FireWire, etc.), you're already set for computer resolutions. Just plug in your computer and you're ready to go.
Let me begin by saying that you can almost always safely show images in 640 x 480, at 60 Hz, from any PC, on any HDTV set. If this is all you need, you don't need to read anything else; of course, that's hardly high-end HD, so I'll assume you went to HTPC for the "more is better" philosophy.
You can output almost anything to an HDTV set, as long as the horizontal scan rate is 31.5 or 33.75 kHz (or 45 kHz if your HDTV can do 720p), and the vertical refresh rate is 60 Hz (30 Hz for interlaced).
Most HDTV sets can safely support 480p, 540p, 960i, and 1080i via analog high-definition inputs. If you are lucky enough to have an HDTV set that supports 720p as well, you also can do 1440i. Horizontal resolution is not important here, as the HDTV set can safely support any horizontal resolution (within certain restrictions, as will be explained later). Here's how these resolutions translate ...