Oh, my system in my sig can play battlefield 2 on medium pretty good, and Battlefield 2142 on medium decent too, but isnce he has $500 you can get some pretty good parts im thinking something like this.
-DFI Lanparty UT NF4 Ultra
-2x1gig Corsair XMS
-Antec Sonota 2 Case with 450watt Antec PSU.
If you need links let me know, that should be under $500.
New build in progress, but this is what I got for now:
-AMD x2 5200+
-Asus M3A78-EM AM2+
-Buffalo 2x1gb ddr2 800
-Hitachi 250gb Sata HDD
-Antec Minuet Case w/ 350w psu
-Windows 7 Home Premium 64 bit