my hyundai w240d, scales very well
you could either use 1-1 pixel mapping and get the 1680x1050 res on the 24" screen or you could let the screen scale itself.
mine does a very good job with both, espeically the scaling. Obviously it wont look as good as native, but its perfectly fine for games.
If you wanted to game at the lower res's why not gofor a smaller screen, or even use a HDTV for gaming (a 720p resolution)
I game at 1920x1200 and I can just manage 60fps with a single 8800GTX on COD4 with everything maxed out @ 4AA and that anti-what-you-call-it filtering, so unless you got a beefy graphics card you'll find it hard to game at 1920.
what are your specS?