My parents have a fairly cheap
model 42" plasma and I was over there on the weekend showing them a few photos from a CD-R disk. Seemed to look OK, but I hadn't sized the images to suit their TV.
I think it will all depend on what resolution the plasma is (as they are not all the same) and then what size you have PP'd your images to be displayed.
If, for example, you have a plasma or LCD with a res. of 1350 x 758, then you'd want to have your images resized to around the same (and no more...otherwise it will need to rescale it (an image on any monitor (or TV) where the viewing size is less than 100% usually results in a loss in visual quality).
Alot of the newer plasmas, which have much better resolution (mainly the HD plasmas - although in Australia what is classified as HD is not, in reality, true HD....except for a rare few which are only just coming out onto the market now & cost $10K +), are likely to show near-quality to a standard PC monitor....which we are all familiar to.
As for the DPI....this is only relevant if printing the image. Otherwise, the resolution (or pixel dimension) is what you need to consider when displaying on a screen.
If I am incorrect....please see my tag line below