I think the clue is in the word 'laptop'. Unless you've got a laptop which has more than one expansion memory slot I seriously doubt if it will support dual channel memory. On desktop PCs you'll find four or more memory slots on the motherboard and using similar sticks of memory in two or four slots enables the use of dual channel memory configurations (if supported). On a laptop there is the built-in memory and generally one expansion slot for one SO-DIMM memory stick. As most laptops are never fitted with extra memory there's not much gain in providing dual channel support.
From your description you've got two memory modules installed already? How many memory slots are there in your laptop then?