A router is similar to a switch, but it performs a number of useful networking functions:
It allows you to create a home network (like a switch), but a router actually separates networks allowing you to share your Internet access without being dependent on one computer's connection (unlike a switch).
You can plug a printer directly into some routers, allowing printer access to any computer on the network.
It provides built-in firewall capabilities that do not hinder network performance.
You can share your broadband connection without purchasing additional IP addresses. (Check to see if your provider allows this.)
For a small network, you generally only need one router, though if you need additional capacity, add a USRobotics 5-Port 10/100 Ethernet Switch. To see how these products work together, check out: USRobotics Solutions.
You can also get a wireless router. It performs many of the same functions, but allows you to combine a regular network with a wireless network.
What does a Wireless Router do?