A lot of games get stretched out badly on widescreen displays.
It would be Super Neat if there were a way to coerce them to run in the middle of a widescreen display (sort of like the horizontal equivalent of letterboxing widescreen movies on 4:3 displays).
I don't know whether this is in general possible. I am pretty sure some video cards have had a mode where they pegged a smaller-than-display-size hunk of display in the middle of a screen one way or another, but I'm honestly not quite sure whether that's a video card feature or a display feature or what. But it sure would be nice.

Some monitors can do this. Also I think most modern graphics cards have the option. If a game runs in DOSBox, I believe there are ini file settings for it as well.

Yeah most of the time its a display setting on the monitor. Windowed mode solves the problem but puts more strain on the system since it has to render the desktop as well (especially so with the vista/7 pretty desktops).
A surprising amount of games can be modded to run in widescreen, have a look at http://www.widescreengaming.net/

Check this thread. There should be a setting in your Intel/Nvidia/ATI control panel. External LCD monitors also have their own scaling settings.

Usually it can be done via the video cards control panel/driver. Just look for scaling options (I know that both Ati and nVidia support this).

Huh...?
Turn it off on your monitor. On every computer I have tried it on, Nvidia scaling doesn't work.

yeah, this works if you have a DVI connection for your monitor. For some reason I don't understand, aspect scaling is not available on VGA connected widescreen monitors (like mine :(

That's because VGA is an analogue signal that can't transmit the necessary data so the monitor stretches the image no matter what setting you have in your drivers; in this case you need to have a screen that can handle that on its own.

Im not talking about using aspect scaling, Im talking about using "no scaling" on both your Monitor and Control Panel.
If you do that your Graphics Card will always send out the native resolution (say 1600 x 900) even if set a smaller one in Windows. It does so by centering the picture and having black borders around it.
But I have to admit I never used a LCD through VGA, but I dont know why it shouldnt work the same. Even across VGA there is a digital link to communicate resolution information (DDC) amonst a few other things

Thanks! In my case, it's Intel graphics on a netbook, so there's neither ATI nor nVidia options.
BUT! Advanced, then go to the Intel stuff tab, then there's a pop-up application, and somewhere around there there's a button of "scaling options". Which includes "preserve aspect ratio" (scale up by the same amount both ways) and "center desktop" (don't scale up). So now I have HOMM3 running a bit small but perfectly clear in the middle of a screen. Woo! Thanks!