which ram would you get for this p4 system

[DCshoeCoUSA]

well, im getting some ram from best buy ... im getting the prices off of their website. which one should i get.

Corsair - XMS 2-Pack 512MB PC4000 1GB (2x512) $350
Corsair - XMS 2-Pack 512MB PC3200 1GB (2x512) $360(why is it more expensive?)

also....... since i would wanna run dual channel................ which would be better? 4x512 or 2x512 with any of the choice above? i know it screams "4x512 duh" but isnt 4 not as good as 2 for dual channeling?

my setup:

2.4c @ 2.9ghz
Zalman CNPS7000B CU
Abit IS7 Mobo
520W PSU
1gb (2x512mb) A-data pc2700 ram
BBA Radeon x800 Pro @ 520/560