I have a similar problem.
Whenever I dial into my ISP with my internal Courier v.everything it connects fine, verifies username and password, and then tries to "register computer on the network." That sounds like DHCP, and sure enough it fails and says my server didn't assign it an IP address.
How do I get it to stop using DHCP or whatever is confusing it? My connection works fine under WIn98, of course...