The 3650 or the 4650 are going to be the best of the best for AGP cards. You really need a fast single core or an early dual core chip to take full advantage of these cards (as per tomshardware.com).
At $170, you could pick up a cheap CPU/Mobo, halfway decent vid card and 2gb of ddr2. Reuse the rest.
Test after test has shown the 3850 is faster than the 4650.. The only thing the 4650 does faster is texture filling.. In actual performance, the 3850 wins..
The HD3850 is the fastest AGP card available.. It's totally comparable to an Nvidia 8800GT or 9600GT although it might
do better than the 9600GT in a few aspects.. To add a little to what Fulmar says: You will need either the fastest P4 cpu available (P4 Extreme 3.6ghz for socket 775 and P4 Extreme 3.4 for socket 478).. Even then, you still won't get to the full potential of this card because those aren't true dual core processors.. Otherwise, it's a waste of money.. If he has 1st or 2nd generation Pentium 4, his options will be very limited and it would be better just to build another system.. He'll have to think about his power supply as well.. The 3850 requires a minimum 450 watt power supply..
