Since the two sets of machines are on different networks, you have to setup port mapping in the base station so that outside systems can access servers on the private-class, internal network.
As far as the base station is concerned, there's no difference between the systems connected to the hub and any other computer out there on the internet, so the router/NAT/firewall aspects of the base station kick in.
It would be simpler (and safer) to reconfigure your network so that all the machines had private-class addresses protected by the base station's NAT and firewall setup. Then all the machines would be on the same (internal) subnet and would be able to talk to each other without any restriction. If you have the rev2 base station (with dual ethernet ports), it's a simple matter of connecting the wired systems to the LAN port on the base station and changing them to use DHCP.