I have an early 2009 iMac with a 1 TB Hard Drive I am considering upgrading to 2 or 3 TB. The main reason is that I had to offload my itunes library due to space issues on my iMac. The main reason I would like to have more space internal is when using Apple TV, it seems like now with my library on an external drive, I always have to restart iTunes and sometimes speed to display photos/videos on my Apple TV has gone down. So my main question is what kind of hard drive should I purchase? Will replacing the hard drive void my AppleCare that runs through March 2012? Is there a better external drive I should be using than the old 640 GB Western Digital My Book? Thanks for the help!