I'd just add -
1024 x 768 is more than acceptible for most purposes. You can get away with 720 x 480 - depends on what compression you use.

In theory you can go to a maximum of 2048 x 2048, but these size images take a long time to load.

If you are doing a range of stills it makes sense to render these as a Photo-Jpeg movie. Photo-Jpeg is not resolution specific (like DV NTSC/PAL) and has much better and cleaner colours. Photo-Jpeg movies load a lot quicker than still images. Use the Inframe function to select the still you want.

For high quality I sometimes use Photoshop (.psd). This is useful as Photoshop is a lossless codec and it saves alpha channel information, which you can make use of in Catalyst.

As mentioned ealier - dpi is of no consequence. It's for printing.

Hugh