ddr1 ddr2

Well, the mos important thin you should check is you motherboard. It'll tell you. But if you use DDR there's no way you can replace it DDR2, sorry... In order to do that you'd have to change your mother board... and with new motherboard along would come new proccesor (because of different socket) and graphics (mboards with DDR slots have AGP instead of PCI). I thought about it some months ago because DDR2 are like two times cheaper than DDR but I dropped this idea.