You could make a custom resolution. Most newer games support a wide variety of Rez's.
But since they have a different aspect ratio and theres no way to change field of view (FOV) on two different parts of one rendered scene, you would have a messed up display.
EITHER: The wide would look crunched or the full would look stretched.
Probably better to go with two of the same aspect ratio and size.
I never liked the idea of two monitor gaming anyway. You got a great big line down the middle. Right where you wouldnt want any obstructions. Matrox tried to do three screen gaming but that didnt exactly take off.
HOWEVER, if you are just talking about your dektop and using two displays for web browsing, image manipulation or multimedia viewing, then it would work fine. I have seen many folks do that here on Anandtech. Do a search for "desktop" and you will find a bunch of threads with photos of all kinds of monitor setups.
Most of the guys are kind enough to show images on their monitors so you can see how it works.
I have this bad boy myself, and its more than good enough for daily office tasks.
http://pics.bbzzdd.com/users/shortylickens/DSC00204.JPG
I still use a quality CRT for gaming.