I am not sure what the last guy is talking about, but here is the topic as I understand it.
Many routers have built in switches, but not all. It is a good selling opint, so they will make it clear if they have one or not. The next thing is that a switch is similar to a hub, but there are some major differences. For instance, a hub sends the information packets to all ports. This can cause extra traffic that isn't need. A switch will send the information only to the port that te packets need to go to. Also, hubs all share the same bandwidth. So a four port 100baset will actually only have 25mbs transfers. Switches all have independant ports, so the 100Mbps is for EACh port. Then most switches also handle full duplexing (sometimes called 2000MBs, though they really just add the traffic both ways) As for the router, it just directs the traffic to the computer that requires it. Though, I would suggest you keep the two seperate. Get a cheap router, and spend more on the switch. If you leased another IP from the DSL company, then all you need to get is a switch and you are good to go. Good luck.