Not full-screen full-screen, better see for yourselves!
http://i169.photobucket.com/albums/u222/Chackankun/Untitled-18.jpg
This only happened with Under a Killing Moon, since i'm yet to finish downloading Overseer.
Any idea?

You've tried pressing ALT-ENTER, right? That's the hotkey combo to get fullscreen. If not, try going to the game options instead and resizing it there.

I'm having the same issue in XP. Alt+Enter doesn't work, when the game starts it tries to go into fullscreen but apparently fails and falls back to a small window. There is now way to tweak this from the ingame settings as it is already set on the highest possible resolution (640x480).

you probably need to play a bit with the dosbox settings.
like output=ddraw
and fullresolution=0x0
and aspect=true (or false dunno)
(this is for UAKM, Overseer is a windows game)

It happens the same with Overseer. Just tried it :|

When you say "not fullscreen fullscreen" you mean that the game run in fullscreen but with a black stripe on each side (like your screenshot actually shows)? Because this is normal behavior considering that none of these games were designed for widescreens they are displayed at their normal 4:3 aspect which leaves two black stripes on the sides.
Depending on your video drivers you might have an option (within the video drivers) to display applications using the whole screen no matter what the original aspect is but in this case you'll experience a distortion of the image.

Yes, exactly like the screenshot shows.
It's weird because it didn't happen on Vista :|

Why on earth would you want to play the game stretched out to a 16:10 aspect ratio? The game was designed as 4:3.

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