Scuzzbuntu: were things also working fine for you, but then stopped for some reason? Does spoofing a MAC address make any difference? And just to confirm that you have the same exact hardware, your "lspci -nn" output includes this exact line:
02:00.0 Ethernet controller : Broadcom Corporation NetXtreme BCM5754 Gigabit Ethernet PCI Express [14e4:167a] (rev 02)
If all of the above is true, then I would assume this is a hardware (and/or driver)-specific problem, though that still doesn't explain why the connection apparently worked fine at one point, but then stopped, and still fails under an older live CD.
If this is indeed a hardware/driver problem, then it might help to try driving the card with ndiswrapper instead of the native Linux driver. You'd need to blacklist the tg3 module, which is the native Linux driver for your ethernet card, and then install ndiswrapper and load Windows drivers for your ethernet device into it. You should be able to find instructions to do all this elsewhere on the Internet, but let me know if you're unable.
Also note that you'll probably find ndiswrapper discussed in most contexts involving wireless cards, but it should work for ethernet devices just as well.