i'll say what core components i reccomend to play BF2, farcry, HL2, and other modern games:
-a64 (90nm process, NOT NEWCASTLE) 3000+ or higher
-1 GB DDR400, dual channel
-name brand (asus, gigabyte, msi) motherboard (i reccomend the ASUS A8E or any variant thereof), your board should be based on the nforce4 chipset.
-a graphics card that is based on the nvidia 6600gt gpu or better, 128mb memory is fine. before you buy, check out the component clock speeds and compare them to the nvidia reference specs, the card should be at least as fast. i reccomend the MSI NX6600GT card, available for both PCI-E and AGP interfaces.
-a quality name brand power supply (from antec, thermaltake, enermax for example) with a watt rating of 480w or better.
the problems with your current setup are the cpu, ram, graphics card, and motherboard, so this major upgrade would give you the abilities to play pretty much any game currently in existence, and will provide some options for the future as well.