I'm gonna disagree partially... The better res you record in the crisper the picture will be. Your video player will play it fullscreen no matter what res it is.
Most carpc's run at 800X600 unless you ave a special video card to run 800X480. The reason is becuase its larger and easier to see.
Example... Watch a DVD on your carpc, then your bigscreen tv. Those DVDs are at a HIGH res and it will look great both paces. Now record something in 800X600 res and try to watch that on your bigscreen....lol.. you'll see square pixles all over the place....
So record at the higest res possible everytime, unless space on your media is a concern.