yeah your mobo has to support dual channel, i have two 256 ddr333 sticks that are entirely different brand names, and purchased a year apart. i pluged them in to my mobo and it automaticaly assigned dual channel, works fine. although i heard that both dimms need to be identical sizes, i havent experimented with that yet but even so if they do work with different sizes, by logic, 2 of the same size woulb be more efficient that two different sizes.