On the left side of the screen it should detail not just the memory type, but the number of slots and the max memory config.
Eg:
Originally Posted By: Crucial
Memory:
DDR2 PC2-5300
Memory Type: DDR2 PC2-5300, DDR2 (non-ECC)
Maximum Memory: 4GB
Slots: 2
Each memory slot can hold DDR2 PC2-5300 with a maximum of 2GB per slot.


Some of the Dell Precision laptops, and presumable similar systems from other makers, have four memory slots, but they are very much the exception, so I doubt the MacBook has more than two. In any case, nice score!