That's DDR memory.

http://www.crucial.com/uk/systemscanner/

use this, scans your motherboard and tells you what type of memory you need and how much you can bang in there and in what combinations etc


It's great memory too, cant fault it. Better than that OEM unbranded shite you get from ebuyer and the like

EDIT - Doesnt work in Mozilla (It uses ActiveX) - make sure you run the link from IE6 or IE7