burkjon: Video drivers do not have an option to specifically force 4:3 (oh how I wish they did), only an option to maintain the aspect ratio. If DOSBox or ScummVM are not forcing the image to be 4:3, it will still be stretched because 320x200 is a 16:10 resolution.
edit: woops, this has already been addressed days ago. Oh well - I should look more carefully next time 320x200 is actually a 4:3 resoluion - it just doesn't seem that way because the pixels are nonsquare, so the dimensions are expressed in mixed units. 320x200 has an aspect ratio of 16h:10v, where (h=horizonal pixel width), (v=vertical pixel width) and (5v = 6h), so:
16h:10v = 16h:12h = 4:3
If you want to integer-scale up 320x200 while preserving pixel shape, thus not distorting the image in any way, then you'd need to go for 1600x1200, which was very convenient for us until the ironically-named HD came along and stole our pixels :p