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.
type "sudo more <filename>" and give your password when asked to. On Ubuntu systems "sudo ..." gets around all restrictions like that, so be careful.
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.
The Gigabit X58 series all seem to have onboard ethernet, so I would expect the BIOS to find that before an add-on card, so the LAN would most likely be eth0 and the wireless eth1.
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.
I would try it with the wireless card removed, in case it's an ISA/EISA problem. You did say that it's an old card.
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?
X58s have been around for nearly two years, so I'd be surprised. Just one thought, some Linux distributions are built in different versions for up to 1Gb of memory, and more than 1Gb (Fedora perhaps?). Is the Ubuntu you're using a full 64-bit, unlimited memory version? I use magazine-cover copies, but I'm careful to make sure I've got the right one for the architecture, AMD 64 bit, or i386 depending on which of my 4 machines I'm installing on.
'b