What's his budget and what games does he play. What resolution does he game at?
In general AGP cards rank starting with the best:
X1950XT
GF7950GT
X1950Pro/7900GS
X1650XT/7600GT/7800GS
X1650 pro GDDR3/7600GS
etc.
There are also the ATI X800 and X850 series I left out since they are getting har to find new and don't support SM3.0. Fine cards if you are looking used and don't play one of the few Sm3.0 only games.
Personally, I would pair a P4 3.0GHz with a X1950 pro caliber card you can play at higher resolution and/or with more eye candy.
Price wise the X1650XT is one of the better AGP bargains since you have a 600W PSU. This ice quiet card recommends a 450W PSU with 30amp 12v rail(s).
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161064
$40 more gets you a better performing card, although we have heard some talks about stability problems with some of them. I would still buy this card without hesitation. Probably most peoples issues are due to infuffienct PSU, but can't rule out card/heat issues for some people. Just a warning, but again it wouldn't stop me from buying it.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161070
Most other X1950 pro's are $200+, same with the 7900GS. The 7600GS and 7800GS are in the $160-170 range, same with the 512MB X1650XT. You have alot of choices, but without knowing the budget and games, it's hard to point you toward any one of them.