so if I understand this correctly, you have a 5 port mini hub connected to the cable modem and then the 2 computers to the hub. Only one of the machines is working. Sounds like you have an IP issue. The router/hub issue sounds close to true, cause the router would assign IP's out to the machines.
Check the IPs on the two machine, because one will get the assigned IP from the Cable company and the other will get a reserved address. This is most likely the problem you are having. Proxy software will enable you to work, but a router is a better option, just cause it's simple.