Hmmm, what about those - don't know what they're called - USB-to-USB adapters that allow you to network two computers over USB?

Would mean no requirement for an extra ethernet card in the computer you attach to - mind, I have no idea how the networking is handled over USB in WIndows (or if it works in other OSs if you need that...) so can't say if it affects the machine you connect to, and/or if it can route between the USB connection and the normal ethernet card. Just an idea, as I saw one of these in a shop yesterday...

/Michael