It did not happen with the same machine's previous kernel, which my backups indicate was 2.6.32-30 (and to which I'm planning to revert if it continues crashing).
Instead I tried the corresponding 486 kernel (i.e. linux-image-2.6.32-5-486 2.6.32-34squeeze1). The system has now stayed up for over a week.
ttfn/rjk