set it to 1:1 and play your game in a tiny box in the center of the LCD
set it to aspect ratio and play your game in a larger 4:3 box going top to bottom on the LCD but leaving black bars on the side
set it to stretch and play your game stretched to hell filling the whole LCD
The above depend on which options your LCD has. Graphics card can possibly set this also.
I decided to play through Starcraft again after all that Starcraft 2 madness. The game only runs in 640x480, and playing on a 1920x1200 monitor was a bit weird at first, but you get use to it. I just had it on aspect with black bars on both side of the image.