The P4 is old, yeah, but it's not so bad. The 6670 is a good match for it, and he has a low res monitor. Sure he won't be able to play 64 player online BF3 matches, but he will be able to enjoy many, many games.
The RAM thing is true, though it's closer to 3.5gb useable on 32 bit OS. Either way, like I said, he should upgrade with 2x1gb for 3gb total... seriously, OP. Do it.
$23 for the RAM:http://www.newegg.com/Product/Product.aspx?Item=N82E16820161481