the MacBook had been freezing on startup: a graphics card gone bad.
The NVIDIA graphics processors on early-2008 MacBook Pro's were known to fail as early as 2008, and Apple and NVIDIA agreed to effect a free repair within four years from the date of purchase and only if the card failed.
Of course, the law of warranties applied in this situation (the product breaks after the warranty expires), so I would have to pay $320 to fix the laptop. I said that I would think about it, especially after looking at all the shiny new laptops in the Apple Store. (Replacing the soldered card is beyond my capabilities, so a do-it-yourself repair is out.)
I have PC's, an iPad, and an iPhone, and my business needs for a MacBook aren't urgent. Nevertheless, it's disappointing that there's not an economical solution to this problem.
[Update: I took the laptop to We Fix Macs, a long-time Apple repair shop next to the Fry's in Palo Alto. They quoted $450. We're going in the wrong direction.]