The router is likely connected to the wall with the WAN port, so it is establishing a connection in a way that the building likes. The router then creates its own subnet for the LAN ports that the PowerBook likes. This is my observation. It seems possible that the PowerBook could have a static IP that the router allows. As mentioned, verify that you are set to use DHCP without manual address.

Is there a reason that you don't want to use the router? Connecting directly opens you to all sorts of hackery from anyone in the building whereas the router provides a very nice firewall and can split your connection to your PC.