Right, looking at that graphic, you appear to have DDR400 (also known as PC3200).
BUT, and that is a big but, I suggest you check out
www.crucial.com and run their memory advisor tool from their homepage before trying to stick anything in your PC.
If you can take PC3200 you should be able to take PC2700, which although slightly slower it's something I've got sat at home. But run that tool above first and let us know, it should let you know exactly what type and how much you can take!
