OK so a colleague explained it to me. Apparantly xrandr comes with almost all linux distributions. The proper way to use xrandr to set multiple monitors to display a different part of the same desktop is as follows:
xrandr
Shows you the names and dimensions of your displays. Say VGA1 and VGA2. Then if VGA1 is the screen on the left and you want VGA2 to extend it to the right you use:
xrandr --output VGA2 --right-of VGA1
Thats it. Was looking for this on google and SO for hours, finally its working! Hope this will help other people as well. Dont know how to save this setting yet and I dont know if this is the most elegeant/best way to do this.
When you know the answer its easier finding other answers. Here are two sources that show how to save this setting as well. (although that does not work on my system as the files they point to cant be found)......