Linksys BEFSR41 is what I have been using with no problems. Its a router with built in 4 port switch. The manual will step you thru setting it up. Basically you need a nic card in each computer, Cat5 cable for each computer and one from the modem to the router.
You can open up ports to certain computers for the programs that need it.
Just use the isp connection program to connect thru the modem.
10/100 will be fast enough for you.