Apologies if this has already been posted, but there's a very good website at
iFixit: Apple Mac, MacBook, iPod, and iPhone Repair Parts which provides step by step instructions on how to replace nearly any part in nearly any mac- although sometimes it's a case of "easier said than done". Remember that Mac internals are not designed to be prodded routinely- antistatic precautions and a lot of restraint in the face of adversity is required!
