Is there an easy way to set the resolution based on what the original should be?

[spongebue]

Ok, here's the deal: I am using a fairly big (~20") VGA monitor, but it cannot go to 320x240 or whatever it is that most games go to, since the minimum resolution is 640x400.  I changed the resolution to 640x480 in the mamewah mame configuration setting, and fullscreen games now work dandily.  I'm a bit disappointed, however, that vertical games are quite a bit shrunk down.  They aren't super distorted as I originally predicted, thankfully, but they aren't very big, either.  Is there any way to have it look at the resolution, determine its orientation, and scale accordingly?  Any help is appreciated.

Thanks,
spongebue