You could also go with the typical cinema screen size letterbox ratio which is 16:9...meaning...anything will scale to that if it's a multiplier of 16:9. The same thing happens with 4:3 (which is what most computer/TV screens are).
1024x768 is a 256 multiplier for 4:3. (4x245 = 1024, 3x256=768).
This doesn't mean anything really, other than making it a bit easier to scale up ratios if you need to. So for example...if I want to work on something that's proper 16:9 ratio...
16 x 64 = 1024 9 x 64 = 576
You could also go backwards..Lets say you wanted to fit a letterbox image to a 1280 width resolution:
1280 / 16 = 80..meaning your height should be 9 x 80 = 720.
Screen resolution for computers is 72dpi for Mac (like Anaphiel said) or 75dpi for Windows. Using either resolution would work just fine, though with such a small difference between then, it's easier to scale up than shrink down, so I agree that you could easily make your images 72dpi for computers.
Hope that helps.