Apparently this is a known bug with the new OS and my model's network card (which looks to be on-board, after taking half the machine apart to get to it...)
Here's what i found out so far: http://www.small-tree.com/gigabit-ethernet-driver-download-a/198.htm however it only applies to removable cards.
This is a massive oversight, i feel. This wee I bought a brand new iPod nano straight out of the loading truck the day they were released (well, almost, it was on the shelf for about a minute) and by the time i get back to my office there's already an upgrade for it's software: yet 10.6 has been out for weeks now and theres no update patch to fix this.
I can download from the internet faster than i can move files across the work LAN.
Hopefully the people at rennaisance have some help to offer, just thought i'd share my tale of woe. Will update as things progress.