Run the game's "Graphic Mode Setup" and set Graphic Mode to OpenGL. Check the Advanced Settings tab and set Scale Engine to "none" for testing. If it works you can try higher scaling.

Close and run the "Graphic Mode Setup" again to check if your settings were saved. If not, run the setup as Administrator (right-click => Run as ...).

nope this didn't work either, it just put it in a small box to the bottom left of the screen (when in fullscreen) and was still overscanned :(

Do you mean your getting a stretched image?. If so use the settings below in your Dungeon Keeper Gold "dosboxDK.conf" file.

[sdl]
fullresolution=0x0 //or... type in your monitor's native resolution

[render]
aspect=true

no, when I play fullscreen part of it's cut off. DOSBox doesn't do this for other games (like Blood) and my PC doesn't do it for anything else :/ I'll try what you've posted and get back to you :)
I've got it to a point where I'm happy with it the settings I used are as follows:

Basic Settings:
- Graphics Mode: Surface (with Fullscreen checked)

Advanced Settings:
- Keep Aspect Ratio checked
- Scaling Engine: normal3x
- Mouse Sensitivity: 75
- Window Resolution 1920x1080

it runs in 1024x768 with a thin black border but it's significantly better than before, thanks to all who helped

Copied from: http://www.dosbox.com/wiki/Dosbox.conf
Surface does not support scaling or aspect correction

I'd change your output to OpenGL and scaler back to normal2x.

Also copied from Copied from: http://www.dosbox.com/wiki/Dosbox.conf
scaler = none | normal2x | normal3x | tv2x | tv3x | rgb2x | rgb3x | scan2x | scan3x | advmame2x | advmame3x | advinterp2x | advinterp3x | 2xsai | super2xsai | supereagle | hq2x | hq3x

Specifies which scaler is used to enlarge and enhance low resolution modes, BEFORE any additional scaling done according to the Fullresolution and Windowresolution settings under [sdl]. To see comparisons between the different scalers, see Scaler.

none: no scaling is performed.
normal: nearest-neighbour scaling (big square pixels).
scan: like 'normal', but with horizontal black lines.
tv: like 'scan', but with darkened versions of the data instead of black lines.
rgb: simulates the phosphors on a dot trio CRT.
advmame: smooths corners and removes jaggies from diagonal lines.
advinterp: identical to 'advmame'.
sai: similar to 'advmame' but with much softer color gradients and edges.
supersai: similar to 'sai' but sharper.
hq: a 'high quality' scaler which delivers a cleaner and sharper image than 'advmame' or 'sai' scalers.

Default is normal2x.

Supported scalers which still need descriptions: supereagle

DrowWarrior is right, that's why I suggested OpenGL before and reduce the scaler, because if you're scaling to a resolution higher than your desktop max you'll run into problems.

Window Resolution is used for windowed mode only, not for fullscreen.

Also check your graphic card's control panel for scaling (see screenshots). Enable scaling and keep aspect ratio if you don't like your picture stretched on widescreen displays.

Here's some pictures of how the scalers look like :
http://www.dosbox.com/wiki/Scaler

thanks for the infos