further to my previous info, the /var/crash files cannot be viewed as they are locked by the owner process that generated them, I forget the name, begins with app something or other.
The DMESG command gives a long script and the only thing that caught my eye is a number of timeouts of eth1, right at the end of the file. I don't know if eth1 is the wired network card or the wireless, can't check without interupting the memory test.
Also, the suggestion that it only crashes when the wireless network is on is a red herring. It can crash before it has even finished booting up. I ran it for about an hour, playing video off USB drive, wireless network disconnected, and it crashed again. When it rebooted it crashed almost straight away, and then after about 15 mins. I tried to send an error report after the last crash and it reported that my copy of Ubuntu is not an original source.
I have, since then, re-installed the Ubuntu to the hard disc, where it failed to boot several times. For over 3 hours now, I have had the machine running the memory test from the first option screen of the Ubuntu Live CD. It has gone through nearly 4 times with no errors.
The machine is an i7 930, with 6Gb ram on a Gigabyte x58 motherboard. Nothing in it seems to be running warm.
Is it possible that Ubuntu 9.1 is just not compatible with the spec of the machine?