Your Actiontec will not work as a router but as a wireless switch in the configuration you are using. Since you probably have only been given a single IP address by your ISP only one computer at a time will be able to access the network in your config. In order to use more than one computer and wireless you need a "real wireless router" so that NAT can be carried out and give you a local LAN.
If your surfboard 5101 had had NAT capability you would have been able to use the actiontec as you did.