It is even difficult putting a new 1,8GHz CPU in your Mac.
I know someone who does these kind of repairs quiet often and he is very handy. He said that the Macs he had repaired so far always had some other problems later, because you have to calibrate the new CPU, after changing. For this you need the Apple Diagnostics Tool CD, that only Apple Techs possess (having this CD, not being and Apple Tech is illegal by the way... I heard).
I do not have experience on this and am only saying what others say!