P4 2.56? Are you sure that its not a P4 2.53? I wasnt aware that a 2.56 existed but i could be wrong. If it is the 2.53 that means its the B revision with the 533Mhz fsb so there is no point in getting Dual channel PC4000 you wont be able to get you FSB high enough to take advantage. (unless of course your very very lucky and ur CPU can overclock to 4.7Ghz).
[Insert witty comment here]