I have one machine on my network that when hogs all the bandwidth when it's on. Any ideas?

The person asking the question had also swapped the operating system on the machine as well from Windows to Linux to BSD – all of which showed the same problem.

My initial reaction is most certainly hardware; I’d swap out the network card and see if that made any kind of difference. I’m guessing it will.

There is one small possibility that it’s an auto-speed sensing related issue. Many network cards can “auto-sense” whether your network is running at 10mbs or 100mbs. However sometimes they get it wrong, especially if they are connected to another auto-sensing device like a hub or router. Getting it wrong could lead to all sorts of odd behavior. See if there’s a way to turn off the auto-sense feature of the card and set it to the proper speed manually.