The Macbook uses DDR2 PC2-5300 Ram, just like the MBP (of that vintage). In order to get 3GB of RAM you have to install a 1GB and a 2GB DIMM, but it won't be dual channel (which means there will be a small performance hit). You could shell out the big bucks and get two 2GB DIMMs, but the MB will only recognize 3GB out of the 4GB. This is an Intel problem, which was addressed with the release of the Santa Rosa platform (now in the iMacs and MBPs).