Hi, all.
I've been using the site for ages, but I've not posted before - sorry about that, but hi.
Hoping someone out there can give me some advice. I've recently bought a netbook with a 1024x600 screen, and I'm having problems with aspect ratios on games. I've been playing lots of HOMM recently (been waiting so long!), but running the default config on DOSbox stretches to full screen, which looks a bit rubbish. I can go windowed, but I'd like to be able to scale it up to full screen, but with black bars both sides where it's maintaining the aspect ration of the game. I've seen a couple of threads on the net which suggest aspect=true and the like, but I've had no joy. Any ideas? Sorry if this is a bit clumsily described, but any help would be much appreciated.
Thanks!

Haven't used any widescreen monitors with DOSBox, so I cannot say for sure, but you could look at this topic on the official DOSBox forums.

Can't you just go maximized windowed mode in DOSbox? Or is that some fantasy?

OK, I think I've got it.
@sheepdragon - thanks for the link - very useful, and not the same advice I'd seen before.
@michaelleung - had a go, but the maximise button was greyed out for me. Thanks, though.
Right, after looking at the thread sheepdragon listed, I've tried a couple of settings and I think this is it:
After installing, open the DOSbox config <install dir>\dosbox<game name>.conf, find the line fullresolution=original and change it to your screen's native resolution (e.g. 1024x600 or 1920x1200). Save.
If you're running XP, that's enough to fix it (how easy was that!). If you're running Vista, you'll also need to launch the 'Graphic mode setup' from the GOG start menu program group. The default (Overlay) causes a crash to desktop for me, so change to OpenGL. With that done, you're good to go.
For reference, I've tested this with HOMM, Cannon Fodder and Duke Nukem 3D on Vista, 1920x1200 and with HOMM and Cannon Fodder on XP, 1024x600. All working fine.
Thanks, all!

The DOSBox forum is a real treasure chest.

Hehe, you would be the one to know.

Glad to see you found it - your solution is specific to only that one application though. If you would like the same behavior in all 4:3 games, including the ones not using Dosbox, try the following: (Assuming Windows XP and Intel graphics, the most common netbook configuration) Open Intel Graphics Properties, select Display Settings, Aspect Ratio Options and choose Maintain Aspect Ratio. This should cause all applications using a 4:3 resolution to be scaled correctly, i.e. with pillarboxing.

Thanks, this just worked for Little Big Adventure.
Strange that you have to set the fullscreen resolution to your monitors native resolution (in my case 1360x768) when you want the game to show in 640x480. I suppose it makes sense but it was a jump of logic my brain just couldn't make.
EDIT: Should've said that Phatman's solution was the one that worked for me.

Actually, you don't necessarily need to do even that. I just put 0x0 for fullscreen resolution in all games, and DOSBox automatically applies the correct resolution and aspect ratio. Works for any and all monitors/resolutions.

That was quite a necropost...

Not at all strange, given that you're not asking it to show in 640x480. That may be the native resolution of the game, but it's not the resolution you're asking it to show on your monitor if you want full screen.

That's really handy to know. Thanks.

I realise that now. Like I said: it makes sense, it's just my brain didn't make that connection. I think it may be because the default option for resolution was 'original' making me believe it was more tied to the games resolution than the monitor... I don't know. Perhaps I'm just a little slow in the head.
Yes, my apologies, that was a bit of a necropost. I found the information that helped me and whether 10 minutes old or 10 years old, good information deserves a little note of thanks in my opinion. After all, people don't need to share their solutions. Just like in that popular xkcd comic.
Besides, isn't that what started GOG? The desire to bring old games back to life? To return to the living that which was once dead and buried? To put your lips to the cold, lifeless mouth of an old game you used to love, pumping at its very heart with your bare hands, screaming "LIVE, DAMN YOU, LIVE!"
And now this thread can once again wither and die, safe in the knowledge that it did its duty. It served its purpose. That someone, somewhere needed it and it was there to help.

I found this thread after having the same issue.

In the end all I had to do was modify one line in the conf file.

fullresolution=desktop

The rest of the options around were already as follows:

fullscreen=true
fulldouble=false
fullresolution=desktop
windowresolution=original
output=Overlay

I found this out after some of the more recently purchased games from GoG allowed you to use the Graphic mode setup to change the aspect ratio. I set one to "Keep aspect ratio" then just compared the conf files.

Interestingly, setting fullresolution=1366x768, which is my monitors native res, didn't work.

I'd pick "openglnb" for output. OpenGL seems to be less glitchy in case of many games and the "nb" eliminates the horrible filtering which normally causes a blurry mess in opengl mode.