I'm sure a 9200 256MB will play HL2 fine, maybe on med settings, no AA, some options turned off, and 800 x 600 res. You can also lower the directX version through the console if he needs to but I think he'll be fine. My friend had an integrated (geforce 4 MX) graphics and it played fine (although it had to be directX 7) with some driver issues.
Just download steam from steampowered.com and download the Half-Life 2 demo and see how it plays.
I know with my P3 1GHz, 256 RAM and 7200 32MB played Call of Duty 1 fine on med settings fine except on the stalingrad part of the game so it should play Call of Duty 1 and United Offensive just fine.
AVP2 will play just fine, I maxed it out with the specs above and I'm 100% he can play it on 'Best' performance like I did.
Also tell us how much RAM you have.