Nope, 2GB is not the actual maximum. 2GB was the max Apple ever officially sold and supported if you bought RAM through them. But the chipset, and OS will work just fine if you put 2x2 into there. It's not going to use the full 4GB, but it will go up to 3GB. I've had hands on experience with this, as someone in my family has this exact model.

This site also confirms it, along with the explanation why only 3GB will be usable. It's our old friend, the 32 bit memory limit cropping up in the chipset, and needing the 3-4GB window for addressing space.

http://www.everymac.com/ultimate-mac-lookup/?search_keywords=MacBook2,1 (Pick one of them then look at the memory section)