Which is better intel gma 950g or a intel g31 graphics chipset...

They are comparable in performance. Both capable to do internet browsing and office work.

Intel GMA 950 - Part of the 82945G Express chipset:
Passmark Score: 120
Passmark Rank: 533rd in the world
http://www.videocardbenchmark.net/video_lookup.php?cpu=...
Intel GMA 3100 - Part of the G31 Express Chipset:
Passmark Score: 169
Passmark Rank: 417th in the world
http://www.videocardbenchmark.net/video_lookup.php?cpu=...

Based on this, I would say that the GMA 3100 is 41% more powerful than the GMA 950 (82945G)

GMA X3100 far outclasses the GMA 950 in performance, but either way, I doubt you'd be able to load Crysis on it.