memory or DDR3 type memory?

DDR3 just means better than DDR2, I'm sure they made a slight change in the technology as well but thats not important, won't make a difference other than a slight boost performance wise, the one thing you do need to pay attention to is whether it is PCI Express or AGP, Motherboards will only take one or the other and if you get the wrong one it won't fit.

DDR3 is faster than DDR2, it would be better to get a card with DDR3 but DDR2 is fine, yes you do need to check the slot type, PCI Express is recommended because it works faster so you get better graphics. I have PCI Express in the gaming machine i built and wow the graphics are really good, so yea if you can get DDR3 it is better.

Essentially graphics cards with DDR3 (more accurately should be called GDDR3) are faster then DDR2 enabled cards.Essentially Gddr3 consumes less power, is faster (usually) and has a higher bit rate processing.

en.wikipedia.org

ddr3 is just slightly faster than ddr2 so not a lot of difference really