With only one IP addy from RoadRunner you will need to have one PC set to DHCP so it auto gets its IP addy from RoarRunner. The other machine will not be able to get online without a second IP from RR however and unless you run two NICs in the machine that is online you will not be able to see either machine.

Thats the sad thing.. you almost have to multihome it without a second IP. You could do what I did and setup an NT server with 2 NICs configure one for Roarrunner and send it straight to the modem then set the other nic for a private net like 10.10.10.10 or something and hook that one to your hub then set your other machines up on the 10 net then config MS Proxy server and everyone gets on

I currently run 4 PCs 2 Notebooks and 2 servers off one RR connection this way. It takes a bit of knowledge to setup but if you have a buddy in the business its a couple hour job.