AMD Athlon X4-640 3.0ghz AM3 - Should run most things smoothly. If you got a good CPU cooler you might even want to overclock it to 3.5GHz.

4gb DDR3 1600mhz - The memory type and speed is good. You should have no problems running any games.

500gb SATA 7200 Hard disk - I'd get at least 1TB, but this shouldn't be a problem.

DVD Rewriter SATA - Kind of requierd if you have disc based games. If you have any games that runs directly from the disc you might want to look at the quality. But since these days games are installed directly on the HDD this shouldn't be a problem either.

Asrock N68 motherboard - Problem, those RAM sticks you mentioned won't work. This motherboard only supports DDR2 ram and with the maximum of two memory sticks. This appears to be a old motherboard and the BIOS is probably shit.

Nvidea GT440 1 GB graphics - Appears to be an old GPU. It got good memory speed and amount. And it supports Dx11. You should be able to run those games. But don't expect it to run smooth on max graphics.

Conclution: Yes, you will be able to run most MMORPGs, CS and CoD4. But Maybe not on the highest graphic settings. In CS and WoW you could probably have it on max graphics. But if in CoD4 and MMORPGs like RIFT and Aion you'll have trouble playing on max.