The best thing to do is buy something like PC2700 or more.. even if you only need less... it's great to have something that is future compatible with higher speeds. when i first got my P4 setup I was using PC2700 even though I really didn't even need more than PC1600!! but for the price difference it's very silly to not get something faster, plus, PC2700 and up is necessary for overclocking thesedays. infact i am going even faster and getting some PC3500 later this week.