You could pick up a cheap socket 939 motherboard on ebay and a cheap socket 939 cpu.

Or if you wanted some future proof you can go for intel core2duo range with a socket 775 motherboard.

The E2160/2180 are decent cpu's. A second hand x1800xt would also do you proud. Or if your after something faster, have a look at 8800gt.

GeiL memory is what i've always used. They are very good. So some GeiL 2gb DDR2 will be fine.