A few of the DOS pinball games use the tweaked 320x350 video mode, which DOSBox displays as doublewidth, but with a ~1.5 pixel aspect ratio. Setting aspect=true makes a big difference in what you see with that kind of aspect ratio. You say you fiddled with aspect, but setting it true should have made the display not so squashed looking.

I tried the demo and the following settings made the game look correct both in windowed and fullscreen on Windows XP:
fullresolution=1400x1050 # or 0x0 or your desktop resolution
output=overlay # or anything else except surface
aspect=true

Maybe it would be a good idea to make aspect=true the default.

Thanks!

'the 'magic' was in:

output=overlay

I found another solution as well: the game can be run in 'low res' or 'high res'
with the later being the default.

running the game in 'low res' let's doxbox autodetection work correctly.

Aspect correction is effective on all available output methods on my Windows XP system with Nvidia gfx. Must be a driver limitation or something.

output=surface
aspect=true

...results in horrible framerate on my 9600GT, latest 181.xx Forceware for Vista x64.

Be sure to set output=overlay or, even better, opengl (or openglnb for no hardware filtering with upscaling). output=opengl had a lot of problems with my older ATI HD3200 though, for some strange reason, might be a Vista x64 thing.