I need to upgrade the ram on an old macbook. It takes DDR2-667Mhz. Although those are quite expensive (guess they are not made anymore?). If I get higher MHz DDR2 memory will it still be compatible and just run at 667? Are there chances that it won't work? Also what about 1067 DDR3?
DDR3 ram is not pin compatible with DDR2 so you will have to find the DDR2.
The higher speed RAM should work as it throttles down to the speed that the motherboard can handle.
The frequency rating on RAM is analogous to the top speed of a car, if it's max speed is (for example) 250 km/h, it can drive up to 250 km/h, but it won't break if u drive at 25 km/h.
Same for RAM. As long as it's the same DDR2 Standard, it will run, regardless of how high the max clock speed is.