The Gateway TVs really are a fantastic deal. They have just about every input you can imagine. The only problem with them is that they aren't quite HDTV resolution (except for the 50" which is what you're looking for anyway).
Actually, looking at the specs on the Gateway 50 inch plasma TV, it also does not do HDTV resolution either. From their FAQ...

The onboard digital scaling engine accepts various computer signals and maps them to fit within 1366 X 768 pixels.
So it's got the same limitations regarding HD resolution as the LCD/DLP rear-projectors.
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Tony Fabris