New Ports
Well I've splashed out on a PCI card with 3 USB 2.0 ports, and my network adapter is now working perfectly. I still don't know what the problem was with the built-in ports, but who cares? Its working now.
I've also significantly increased performance by installing the latest Nvidia drivers. The OpenGL based screensavers, which were crawling, are now running at full speed. Also, basic things like moving or resizing a window now happen just as quickly as they would with Windows. Installation was straight forward, using the Package Manager, but I did have to venture to the command line to run an activation command. Whilst this was fairly simple, I would have thought the package could have been configured to do this automatically, or at least ask if you want to do it, and then run the command for you.