I made some more searches. I report the results hoping they will be useful for somebody else:
The most part of mobo with G965 chipset are uATX form (including P5B-VM), while the gigabyte
GA-965G-DS4 is ATX form. I found also two intel mobo ATX form with G965 chipset, DG965RY and DG965RY, but it seems to me that GA-965G-DS4 has more features at about the same price.
The intel open source drivers should be supported by xorg starting from 7.2 release:
There is also a project to build open source 3D drivers for nvida graphic cards:
For a preview of these drivers, again phoronix:
So, if what I've understood is correct, the possibility to run open source drivers on both the two systems I'm considering to buy will be a matter of time. Now I can not decide if buy core 2 duo or athlon64.
Is somebody running the GA-965G-DS4 and can tell me this board works without problems under Linux? I've already made some searches and I didn't found any particular problem.