What is this PC for? It's quite ancient.
For that motherboard you need DDR2 RAM. But DDR2 is ancient and thus it will be both harder and likely more expensive, if you do find it.
So instead, you ought to upgrade your board to something newer, such that you can use DDR3 or DDR4 (coming soon) RAM.
This will allow you to equip a better CPU as well and get a better experience.
So what's your budget?