The problem was that the OEM 120 GB HDD on my 2007 Macbook Pro was getting uncomfortably full. I bought a 750 GB replacement and installed it myself, since my self-respect precluded paying someone else to do it. So did my budget, for that matter.
The process of swapping the hard drives was pretty straightforward. After watching the relevant iFixit video and printing the procedure, I found everything went very well and as expected. The whole exercise took about 20 minutes and went without a hiccup. Like mercury on polished ice, although this was my first time changing a Macbook hard drive. In fact, the only tricky bit was knowing which screws had to come out, and the iFixit materials had that covered. I was a little concerned because I didn't have a spudger at that point, but used a very thin-bladed knife to get the job done. Yeah, I know some would say that was a poor idea, but my options were limited and great care was taken. All's well that ends well.
Trust the iFixit procedure, as it was complete and correct.