tests for bad hardware

[Barry]

I have an intermittant problem with a laptop running Ubuntu 6.06. It's
got a Core duo processor,  2 gigs of ram, a sata drive, an Intel board
and an nvidia graphics card, and want to know if there are any tools
that can scope out bad hardware. I know of memtest86, and the results
are below.

Every time I've run a program that is memory intensive, the machine
crashes. It just stops, as if someone pulled the plug. Nothing is
written in the logs to indicate what the problem is. This has happened
about six times. In between these failures, the machine runs fine --
i.e. when I use it as a lightweight desktop for Firefox, T-bird,
rhythmbox, gnome-terminals, and occassionally OpenOffice and Gimp.
It's generally up 24 hours a day (without the battery in), and shows
no sign of trouble until I do something more demanding.

One day, I did an extensive test with memtest86. The ram is in two
modules so I was able to test one, then the other and both. With both
modules in, the machine crashes early in the first iteration -- just
like the other crashes: pffft and the machine is dead. There is no
report of problems before this happens. I have to restart to get the
DVD out. With either module in, memtest will do one or two iterations
successfully, but it crashes with each one after a few loops of the
default test set. I suppose memtest is exposing some other hardware.

Any ideas?

TIA