1920 X 1200 is the resolution you wanted for the 24" monitor. The old 1600 X 1200 would make everything looks flattened. So what if my highest resolution is 1600 X 1200? The solution is that you need to update your new driver. Here is how you can do it on Vista.

 Right click on mouse, click Personalize->Display Settings ->Advanced Settings ... -> Monitor -> Properties -> Driver -> Update Driver ..., automatic updating should usually work.

 Then you should find the 1920 X 1200 as the highest resolution, select that and you should see everything clearly.