http://text.dslreports.com/faq/9402
Q: How to setup the 5100b with a router/hub (#9402)
A: If you want to network your connection with the 5100b you will need a router. The 5100b hands out only one LAN IP address (and does NAT) so a hub will not work. There are two methods you can use to network the 5100b. While initially, The first was the recommened version, as time went on, and users and support got used to the idea of PPPoE on the modem, the second approach has become the preferred method.
Method 1 (Single NAT) –
1: With your computer plugged directly into the modem bridge the modem using the FAQ entited How can I put the 5100b in bridge mode?
2: Plug the router in between the modem and your computer.
3: Set your router up for PPPoE and put in your full e-mail address and password. If it asks for an IP address or anything like that you can just leave those fields blank.
4: You should now be online, given the possible need to restart your devices.
Method 2 (Double NAT) –
1: With your computer plugged directly into the modem follow the FAQ entitled How do I setup the 5100b to connect to the internet?
2: Plug the router in between the modem and your computer.
3: If your router has an IP address of 192.168.0.1 then you should change it to something else like 192.168.2.1. 192.168.1.1 will work, but if it assigns 192.168.1.64 to a device, it won’t route correctly, since the 5100b will assign the router 192.168.1.64 on its WAN side.
4: Setup your router for DHCP on the WAN side, or set it statically to 192.168.1.64 with a subnet mask of 255.255.0.0
5: You should now be online, given the possible need to restart your devices.