RAM Type: PC2-5300 DDR2 Min. RAM Speed: 667 MHz
Details: Supports 667 MHz PC2-5300 DDR2 SDRAM.
Standard RAM: 512 MB Maximum RAM: 2 GB
Details: 512 MB installed as a single module. One slot free.
Also see: Is the 2 GB maximum RAM capacity for the MacBook Pro a true limit? Would it support 4 GB of RAM if I installed dual 2 GB SO-DIMMs?
http://everymac.com/systems/apple/macbook_pro/faq/macbook-pro-maximum-ram-capacity.html