Hi!
red_avatar is right. You should be looking for drivers.
I recently had the opportunity to test both Catalyst und ForceWare regarding interpolation of non-native resolutions and if it can be customized.
First of all, let me point out, that the form factor of the LCD is also very important. Most 19" LCDs have a native resolution of 1280x1024 (so, you are not getting a 4:3 screen, but a 5:4, which would make its dimensions more quadratic compared to the TV-like aspect ratio). The same applies to 17" LCDs with that resolution.
You should also pay attention that you get a display with a digital graphics port (DVI) and make use of it. There are several versions of this connector, one of which is not desirable because it is only analogue (DVI-A). Just go look it up on Wikipedia.
Most LCDs have as good as no options or menus to affect interpolation and scaling behavior in any way, so tweaking drivers and software is the last resort.
ATI Catalyst
With the ATI drivers, it seems that DVI is a must, otherwise you cannot affect resolution scaling in any way. There are two options:
1. Center image without scaling (That would leave a big black border around any common DOS resolution.)
2. Stretch image to fit screen. Regardless of what you have (a 5:4 screen or a 16:10 screen, even), your DOS game would be stretched to fit its dimensions, thus not maintaining original aspect ratio. If you have a 4:3 LCD, you are in luck, though.
Adding to this, I have found, that the first option not always works as expected. If I choose a desktop resolution of 1024x768 the image would be scaled to fit my LCD, although I set the driver to center it.
I even contacted ATI's support over this problem. It definately is a bug, because with nVidia drivers, centering just works. But they didn't really understand me or didn't want to, I don't know. They just weren't able to assist me and didn't really listen to what I had to say, nor forwarded my request to 3rd level support, as I requested, because I am certain it is a bug.
nVidia ForceWare
Luckily now, I have upgraded to an nVidia card (much because of the annoying problem above and because it leaves me some more options considering interpolation). However, I don't know if they also apply to the analogue outputs.
1. Center image (equal to ATI setting 1)
2. Stretch image (equal to ATI setting 2)
Now come two settings that make use of a so called "Internal nVidia scaling":
3. Stretch image using internal nVidia method (equal to ATI setting 2)
4. Stretch image maintaining aspect ratio using internal nVidia method
I prefer option 4 and am very happy with it, since StarCraft and Diablo II for example can now be played in their original aspect ratio on 5:4 or even 16:10 LCDs, thus leaving small black bars at the top and bottom of the screen (respectively left and right borders on wide screens), but isn't that great?
I have tested the internal nVidia scaling with 3DMark06 by the way and didn't experience ANY performance drop. So they must have done it in hardware or I don't know how they do it, but it just works and they somehow have done something right!
Unfortunately, I figured that ATI setting 1 and nVidia setting 4 don't work as expected with a resolution of 320x240. The output is often strangely doubled in height. But this might be a bug of my monitor and I believe, it could be corrected with DOSBox' settings.
So, this all really is a complex and technally confusing matter. Maybe that's why ATI didn't really get what I was trying to explain to them.
I believe pixel-exact scaling is very hard to find and my experiences tell me that no driver or screen supports anything that comes close to it.
Actually, it's a shame that LCDs are so uncustomizable and unintelligent when it comes to interpolation and screen scaling. :( It's all just a big pain and nVidia's internal scaling is the best alternative for us.
Regards,
locutus