HTPC is short for Home Theater Personal Computer. The biggest advantage of a HTPC is you can custom design many different output resolutions to tailor specifically to your display device. For DVD playback you would be hard pressed (read:impossible) to get a better image spending the amount of money on a scaler that you would on a HTPC. It wins the bang for the buck race all day long. That said, I use my filter modified Quadscan most of the time, go figure.
HTPC is a home theater computer. You could put together a computer download some software. Buy a good video card like a Radeon and a good sound card like an M-audio. And have it scale your dvd's to the sweet spot of your projector and be a Dvd player all in one.
If you have more questions I would suggest spending some time at the HTPC forums.
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