You're welcome.
Well, I can't speak for a plasma screen, but I have a projector and a Radeon equiped HTPC, and the images are stunning in comparison to a standalone player.
The graphics card you have is good, but can be prone to banding where there are gradients of the same colour. An example opf this is the beginning of Titanic where the sub slowly sinks into the water - instead of a blended light blue to dark blue transition, you can see distinct rings of blue.
But, I would suggest you try the pc first, just to see what the results are like, then consider upgrading to a Radeon. If you play games, then a higher end Radeon will be better than something like a VE or 7000 model.
PC output is progressive by nature, so you'll have both NTSC and PAL progeressive.
Some people have problems with PowerDVD, so maybe try WinDVd if you do.
DScaler is freeware, and works with capture cards like the Pinnacle PCTV Rave. It will scale the input of the s-video and by using some of the options can produce an excellent picture. The PCTV Rave card can be bought from around £30, depending on where you get it.
Chances are that the scaler in the Plasma won't be as good as a Radeon (can't say about your GeForce), so I would think that the PC would be the best method of scaling to fit the screen resolution.
It wouldn't hurt to try playing a DVD via your PC first, just to see what results you get. Make sure the output is 1024 x 768 of course, otherwise the Plasma may try to scale it to fit, or you might just get a big black border round it if you're giving it a smaller resolution.
Gary.
__________________