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Very straight-forward. Use the tear-apart instructions at ifixit.com, be certain to use the correct size cross-point and torx drivers, available at Radio Shack and elsewhere.

Fifteen minutes plus restore time.

I printed all the photos, poked holes in the screws on the photos, and put the screws in the holes so that I wouldn't mix 'em up.
 
Does it void the warranty?

In theory yes: it's not a user serviceable part. In practice as long as you are careful and do not damage anything then it may or may not. Clearly Apple will no longer cover the drive as it's not the one they sold you. And anything you move or displace in doing it will probably not be covered as Apple can easily claim you damaged them (which you might have). As you do not need to touch or move the logic board this should still be covered.
 
Your Macbook Pro has a written warranty that you should read. In the US, the Magnuson-Moss act is also relevant, you can read it on-line.

You'll read advice opposite of what I post below, refer to the two documents above if it's not clear.

1. You don't "void" your warranty by installing anything, regardless of what anyone on a forum, on the phone at Apple, or in an Apple store might tell you. Read the warranty, read the Maguson-Moss act.

2. If you have a problem with your Macbook Pro in the future, and Apple believes that a modification you made caused the problem, they can deny warranty coverage. If you replace your hard drive competently with an appropriate drive (similar interface, size, heat output, weight, and power draw), it is unlikely that Apple will believe the drive caused a problem with anything other than the drive or the drive controller.

Good luck.
 
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