Hard drive is an easy swap.
I buy all of the cumputer equipment for home and the shop from New Egg. Good prices, great service.
If you can keep the drive going for a bit you can actually "clone" the new drive to match the old one. You need to download a trial copy of Acronis True Image. Then get your new drive connected to the computer and run the cloning feature.
Takes about an hour or so depending on how much data and how well the old drive works. Once complete swap them and you will be in business.