Honestly, his system is very similar to what my old one was (replaced Jan 07). It ran AH fairly good (it would dip into the 20's when flying near a smoking base with lots of cons) otherwise 40-50+, no high res packs but I believe I ran it at 1280x968 or whatever. I had P4 (Northwood 533mhz FSB) 2.8ghz, 1gb DDR 333mhz, and an 5900XT.
He's most likely has a Pres
Hott, and DDR. Although I can't say if its dual-channel or not. My Asus P4S8X board circa 2003 did not have dual channel. He has an AGP card so it makes no sense to recommend PCI-E cards (your Nvidia 9600's).
My opinion is that adding 1gb of RAM (dual channel sticks or just 1 stick) and upgrading the graphics card could make a nice difference. The amount of ram in that computer and that terrible FX5200 are really holding back that P4 CPU. For +/- $100 you could see a marked improvement for the short term if you mainly play Aces High.
SAPPHIRE 100175L Radeon X1650PRO 512MB 128-bit GDDR2 AGP 4X/8X Video Card - Retail - $62.99
*I went with this card because of PSU limitations. He did not say what he had but the 1650 needs a 350 watt PSU which is reasonable and this card won't break the bank and/or be too powerful for the old P4 cpu.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102073 WINTEC AMPO 1GB 184-Pin DDR SDRAM DDR 400 (PC 3200) Desktop Memory - Retail $18.99
* This is pretty cheap for old DDR and you could buy 2 if you motherboard supports dual channel. Totaling your system at 1.5gb or 2gb. Granted dual channel would give you a performance boost, but its not gonna make or break the system if you're in a bind.
http://www.newegg.com/Product/Product.aspx?Item=N82E16820161626Now I only recommend these upgrades if:
A) You main game is Aces High and you spend a great majority of playing it and will continue to in the future.
B) You're on a budget and cannot afford a new system in say 5-6 months time.
If you say no to any of the above, then I'd recommend saving that $100 and waiting to get a whole new system which depending on what parts you reuse, can get a nice gaming rig for $400-700.