Wounded Ethernet

Does anybody know if it's possible to replace the built-in ethernet on the Powerbooks?  Mine seems to be having trouble passing more than about half the data it tries to send or receive, meaning that about the only thing it's useful for is pinging another computer at this point.  Frustrating, because I can't get Maryland's wireless to work either most of the time, and I can only use my laptop to print if I'm on the ethernet connection in the department because of a firewall.