Getting tired of explaining how to set up weapons groups (WG) in the game, i thought id make a little tutorial, so next time i just can point out this thread.
German version here
1. Go to the control panel, select Options > user interface
2. Select at least 3 keys for Assign weapon group. Preferrably you should take the numbers on the number block of your keyboard. If you have a number block, of course.
3. Select another 3 keys for Activate weapon group
4. Go to Ship controls and select the keys for firing the weapon groups. Group 1 will be guns, this will normally be the right mouse button. For the other 2 groups, pick a key you dont have to break your fingers to reach them. But finally, your setup must work for you, so youll have to figure out yourself which way works best.
5. Close control panel and open the weapons list in the lower right corner of the screen. Deactivate all weapons (they should be light blue now)
6. Hit the Activation key for WG 1. Nothing should change, all weapons should be light blue. Now press the key for Assign WG 1, keep it pressed and select all the guns in the list.
7. Hit the Activation key for WG 2. Again, all weapons should be deselected now. Press the key to Assign WG 2 and keep it pressed. Now you select whatever weapons you want in that group.
8. Proceed as explained in 7., but with the keys for the WG 3.
9. Activate WG 1 (this is the one that usually will be activated)
Note: It doesnt work always on the first go, dunno why. But usually it works after one or two retries.
10. Go out there and blast them all to pieces
11. Repeat 10. ad libidum 
