You can set up your base station or your Time Capsule to share a single IP address with all of the clients on the network using Dynamic Host Configuration Protocol (DHCP) and Network Address Translation (NAT).
If your base station or Time Capsule uses PPPoE to connect to the Internet, it already shares a single IP address using DHCP and NAT.
Open AirPort Utility, located in the Utilities folder in the Applications folder on a computer using Mac OS X, and in Start > All Programs > AirPort on a Windows computer.
Select the device you’re setting up, and then click Manual Setup. Enter the base station password if necessary.
Click Internet in the toolbar, and then click Internet Connection.
Choose "Share a public IP address" or "Distribute a range of IP addresses" from the Connection Sharing pop-up menu.
Enabling DHCP and NAT by sharing a public IP address, or distributing a range of IP addresses lets the base station or Time Capsule dynamically and automatically assign IP addresses to client computers, which simplifies each computer’s TCP/IP configuration.