The MacBook Aluminum uses a new high speed form of memory called DDR3-1066. The system maximum is 6Gigs with the installation of one 2Gig and one 4Gig SO-DIMM.
Non-Stacked IC’s: Ramjet uses a Non-stacked module for the 2GB and 4Gig module for the MacBook. The cheaper stacked IC variety of 2GB and 4GB SO-DIMM runs hotter and draws more power, which hurts performance and decreases battery life. Ramjet ONLY uses premium non-stacked chips.
That being said, the 4GB modules currently run at $600 a pop so this isn’t for the faint of wallet. If that doesn’t scare you, why not upgrade that hard drive to 500GB while you are at it?