I'm looking to upgrade my HDTV I have connected to the XRGB mini and am leaning towards 720p plasma sets, although for a good price in good condition I would take a 1080p one. I'm still fuzzy on the geometry of those resolutions.
For example the Panasonic TH-50PX60U says that it is 720p, but that it's native resolution is 768 (like a computer monitor). Does this mean there will be a geometry, or bars? What would happen if you connect a 480p source (like the Dreamcast in VGA mode) to that? What happens when you connect 480p to a 1080p TV? Fixed pixel displays have to use all of their dots, unless they have bar on the top or sides, right? One of the reasons I want a 720p plasma rather than 1080 is because that resolution is a multiple of 240, but if the screen really has 768 dots that's not at all a multiple of 240.
If anyone has an explanation for how this works I would be grateful to read it.
It would scale the image to the full size of the screen by default, but like many LCDs/Plasmas, there would be different image scaling options you could choose between. ('Native, 'Full', 'Zoom', 'Wide', '4:3', etc.)
I don't own an XRGB, but I would imagine you would set the TV to 'Full' and let the XRGB handle the scaling from the source console. The Plasma is able to handle a 720p signal natively, so it would look fine. For what it's worth, most LCDs and Plasmas have a panel that's 1366x768, and are marketed as '720p'. I wouldn't worry too much about it.
Dreamcast's 720x480 VGA output resolution looks great on a 720p panel. The overscan that's outputted via VGA, compensates for the horizontal stretch when displaying it in 'Full' on your plasma, displaying a sort of anamorphic widescreen.