Success!
OK, it took a while to get everything, but I finally did the upgrade.
I put the WD 1 TB drive into a Sharkoon Quickstore Portable Pro USB enclosure that comes with a slider you can remove to accommodate the 12.5 mm height. At first, my MBP failed to recognize the drive at all, whatever I tried (panic!). A friend at work suggested I try it in another computer. I plugged it into my Dell 10v Hackintosh which recognized it immediately, and I then used the Disk Utility on the Dell to format it as Mac OS Extended (Journaled).
The MBP then mounted the formatted WD 1 TB, no problem, and I cloned the MP's 320 GB start-up drive onto it. Then I swapped drives, which was a walk in the park on my 2nd generation MBP, even for a technically-challenged fumble-finger like me. The hardest part was fitting the MBP's battery back into its enclosure.
Here's a tutorial.
When I restarted, the MBP took a good long time to boot up, and I first I thought I was hosed. But after sitting on a blank screen for about 20 seconds, the familiar Apple logo appeared and the boot-up proceeded normally.
It's still early in the game, but I've been using my MBP for a few hours and I don't notice any speed lags, compared to the 7200 RPM 320 GB drive I replaced. Everything I access, photos, applications, videos, loads just as quickly as before, if not more quickly. And I have all that space!
