You need either a router or a switch but not both.
Router requires less work moving from system to system and may offer more features for the price. You can get a wireless router for the same price as a wired router so get a wireless one, even if you only use the wired ports. You would enable DHCP on the router and set each computer or device to "automatically obtain IP via DHCP".
Switch is less work remotely, but requires each system have an IP address that is manually input. You would also need to enable ICS on one of your computers and put a 2nd Network Interface Card into the computer that has ICS enabled. ICS being enabled on your network will prevent most LAN games from working correctly. ICS host will also suffer a 10-20% decrease in performance. Essentially the ICS host system is your router.
You need a Network Interface Card or Wireless card for each computer/device.
Prices:
Netgear 5 port Gigabit Switch at Netgear's web site $45 for the plastic one, $55 for the metal one.
D-Link DIR-615 wireless draft N type router at Buydig.com $47 including tax and shipping in the U.S. has 4 10/100 ports.
D-Link DIR-655 wireless Gigabit Draft N type router at Costco or Sam's Club, ~$90 has 4 Gigabit ports.
I see answers sometimes from people that shirk draft N products because of the future ratified N may not be fully compatible with the draft N of today.
First of all, if you get all of your devices in Draft N today, they will always continue to work with one another from this day forward until they become totally inoperative. Secondly, if the ratified IEEE 802.11N is not fully compatible with the current draft N it will definitely be backwards compatible, because the core precepts and operational specifications are ratified now already. The major contentions are over how many antennae are going to be allowed and some of the other minor issues relating to how the routers will share the frequency bands with existing equipments.