Well several hours of memory testing hasn't shown a thing. 
I'll just have to wait to see what happens next time... 
Thanks for all responses.

Brian.

On 2007.07.06 09:53:29 -0700, Jeff Rizzo wrote:
> My experience with this particular thing happening is that it's almost
> always bad memory.

On 2007.07.07 16:07:00 -0700, Aaron J. Grier wrote:
> the only times I've run into this have been memory (parity) errors on
> older K6 and PPro machines.


-- 
  Brian de Alwis | Software Practices Lab | UBC | http://www.cs.ubc.ca/~bsd/
      "Amusement to an observing mind is study." - Benjamin Disraeli