I'm using an Acer Aspire One 531h laptop. JADG is the first game I tried playing on this machine. The game stutters every few seconds in the main menu and in-game. The problem is worse when I set the graphics mode to Surface, but it gets just slightly better when set to Direct3d. Still, the game is rather skippy to be enjoyed thoroughly
I've tried 2 other games on my Netbook. One is Die by the Sword - that works flawlessly. Another is Beneath a Steel Sky. No sign of any lag for the most part, but when I go into the main menu, scrolling the mouse a little shows a bit of lag, like lower FPS than when in-game
Im posting this here in hope of getting more answers, and also because I'm not sure if this problem is only exclusive to JADG. Help a fellow GOGer out here please :(

I don't have the deadly games but I can guess it runs via dosbox? Then your laptop is probably too slow to handle it since dosbox is a full dos emulation.

try pressing ctrl-f11 once and ctrl-f8 once as well during the game

Type in your config when you ask for lags...

That did it, thanks.

I had same problem, thanks deanco for solution ;)

In the Jagged Alliance - Deadly games folder there is a "graphic mode setup" exe double click this and you get a drop down menu to change DOSBox from surface to overtlay or ddraw, etc. Very easy to try all the options and see what's best for you.