They take 200-pin PC2-5300 (667MHz) DDR2 SO-DIMMs. They can take two 4Gb sticks and see a maximum of 3.3Gb.
I think you mean two 2GB sticks......
MacBooks 2,1 (mid 2007 models) will work just as happily with PC6400 sodimms and these are usually slightly cheaper than PC5300.