Use the following:
fullscreen=true
fullresolution=1920x1200
fulldouble=true
output=ddraw # apparently doesn't work in Vista - try opengl, overlay or openglnb instead
aspect=true
scaler=none

Hey thanks for that, I had no idea the output=ddraw would dramatically change things.

There are a few problems with that though. Firstly, DOSbox writing and games lose their 'sharpness', everything has a slight shadow/blur. Secondly, whilst Zeliard was sized correctly (it seems like Zeliard fits perfectly into 16:10 mode), other games like Master of Magic seem to not be maintaining their aspect ratio, even though it says that are.

I had no idea the output=ddraw would dramatically change things.

Every output driver except "surface" scales the image to fill the screen (from some forum posts I gather that Vista has some bug with ddraw preventing this from working correctly but I can't confirm). "Surface" just adds black borders.

There are a few problems with that though. Firstly, DOSbox writing and games lose their 'sharpness', everything has a slight shadow/blur.

To get a sharp display, you have two options - either use one of the "normal" scalers (normal2x, etc), or don't use any scaler and use output=openglnb instead (some posts on this forum claim that openglnb doesn't work, but I've tried it on Windows XP and Mac OS X and it worked on both).

I would use the output=openglnb approach, because it takes advantage of hardware scaling and it works at any native resolution. With one of the scalers you can only get 2x or 3x (or 4x with Elamaton's patch), with the rest scaled using hardware scaling (blurry unless using openglnb).

Secondly, whilst Zeliard was sized correctly (it seems like Zeliard fits perfectly into 16:10 mode), other games like Master of Magic seem to not be maintaining their aspect ratio, even though it says that are.

I just tested both games at 1920x1200 and Dosbox correctly pillarboxed both. Neither is supposed to fill the whole wide screen, because DOS games were designed for 4:3 displays.

If some games fill the whole widescreen display (when Dosbox is set to fullresolution=1920x1200 or some other widescreen resolution), it's because the games used a non-square pixel mode such as 320x200 (very common), and Dosbox had aspect=false. Aspect=true corrects such resolutions to 4:3 and adds pillarboxing to widescreen resolutions and letterboxing to tallscreen resolutions*. Without aspect=true, 320x200 games are treated as square-pixel games, making them artificially 16:10, and thus filling the widescreen display (and resulting in letterboxing on regular, 4:3 displays).

* I just tried some games at 640x960 (the game takes up only 480 pixels vertically) and Dosbox correctly added thick black bars to the top and bottom. Similarly, Dosbox correctly added thick black bars to the sides at 2048x480 (the game fills only 640 pixels horizontally).

PS. Dosbox might work differently on another configuration (I've tried WinXP + Nvidia as well as a MacBook laptop) for some reason, but I'm pretty sure the way Dosbox works on mine is how it should work.

PS2. I forgot to mention that none of this aspect ratio correction works in text modes so launch a game before concluding from the dosbox prompt that it isn't working ;)

THANK YOU, openglnb worked perfectly without any blurring. ripa, that has to be the most comprehensive response to any question I've ever asked in any forum on the internet. I'm quite overwhelmed by your knowledge actually, very impressive.

I must say that although I'm an aspect-ratio freak (stretching should be banned), I must say that Zeliard works quite well streched in widescreen mode (boxes are square and gem circles are round). Could that be because of the non-square pixel mode you were talking about?

Spot on about the aspect ratio correction not working for text modes as well.

Thank you so much, I can now happily hand over my old computer to my mum knowing that I will always be able run my favourite old games!

Long live DOSBox!!!

Thanks ripa.. good info.