The panel takes pretty much anything, so you can do as you please. French XBOX, Russian XBOX, US XBOX, etc. Don't get too hung up on the 1080p thing. That only means the panel accepts 1920x1080/60 progressive on at least one input.

The actual native display resolution is 1024x768. The pixels aren't square, thus you don't have an elongated image. In practice it looks great, I had an NEC panel with this resolution. For 42", you really don't notice more anyway beyond a few feet.

On the DVD/Home theater system, those specs are only for UPCONVERSION of standard definition DVDs. Thus, it won't play HD DIVX, but will upconvert your SD DVDs (and perhaps DIVX) to whatever resolution. Whether you want to do this depends on whether the player upconverts better than the plasma's scaler works. They both do the same job.

You might try the Mac Mini at 1280x720 resolution to see if you can play HD content. It may choke at 1080p but play fine at 1080i/720p. The Radeon 9200 is pretty slow but may still work.