Try a router/switch combo. I personally use a Linksys BEFSR81, but any should work. Most should have DHCP and NAT built-in, so you use internal IP addresses. For example, I have a desktop, laptop, and XBox hooked up to the router, with DHCP active and telling it to handing out internal IP addresses starting with 192.168.1.10. So the computer (or whatever is the first device powered up and requests an internal IP address) is given the starting IP. The second system gets 192.168.1.11, and so on. If I shut off the desktop, that internal IP is available for use, so if I fired up something else on the network, it'd be given the first (lowest) internal IP address. Really convenient...
All the NAT does is access a table used by DHCP and point that to the IP provided by the ISP, so that your devices can reach the outside world.