Some more (non-)progress.

I have memtest running on the machine.   So far so clean, and I shall
leave it running over the weekend.

But I was able to find the right kind of memory in another machine,
swapped it over and got the same sorts of error.

I've also tried booting from an installation CD, just in case it was a
corrupted kernel on the boot disk, but get the same error.

Given that it's not always exactly the same error, but that references
to clocks and timers are common, I wondered whether it might be
something like the battery for the RTC failing (this is quite an old
machine, maybe five years old).   If I look in the CMOS setup pages
it's ticking away quite happily though.

--
Steve Blinkhorn <steve@prd.co.uk>