if money is enough of an issue for it to be "good enough", then you should go with DDR2 ram.
a top end 2x2GB DDR2-1066 module costs a mere 70$ today. and is only a few percent slower the the DDR3 ram that costs several times the amount. You are better off upgrading your CPU and GPU before upgrading your ram SPEED. (now ram amount, that is a different thing, upgrading the amount of ram is good)