Blayne, if all you need is to know the various pixel sizes (widescreen and standard) to create your desktops at, my site is a pretty good reference (I make everything that is typically used on PCs and most of the weirdo Mac resolutions).
As for "resolution", measured in DPI or PPI... it really doesn't matter. All that matters is the pixel size. A 21" monitor running at 1024x768 has exactly the same number of pixels as a 12" PowerBook screen running at 1024x768, and you can use the same desktop image for either without resizing. The PowerBook has much higher "resolution", but that's a meaningless term until you start to bring an image onto the printed page (try this experiment: make a 1024x768 image @72DPI, then resize it to 100,000DPI and check the filesize; if you don't interpolate it it stays exactly the same, because the number of pixels is the same).
FWIW, I usually make desktop images at 72DPI, so if you look at them in most imaging program you don't have to zoom in to see them in detail. It's a convention going back to the early Mac days I believe.
