By far the simplest route is to use MAC address filtering simple as, that way you don't need the overhead of encryption unless you want it of course!

Should be simple enough to configure via your router, from a cmd line type IPCONFIG /ALL then look for the Physical address which is 6 sets of Alpha/Numeric digits you simple add them into your router and your away

This only restricts wirless devices anything plugged in via an ethernet cable works as is.