Broodwar always runs @ 640 x 480 which is a ratio of 4:3. If you use it on a larger screen, it usually is scaled up to use as much of the screen as possible.
Your resolution is not 4:3. So you either have to stretch the game to fit into your resolution (ugly) or you will get black broders.
If you are talking about SC2, it should work well with any resolution that is at least 1024x768.