these guys have given alot of examples for you to check out...

basic idea 1st - get to the settings of your router (configure it as needed) 192.168.1.1 (this is the common ip for linksys systems through the browser)
2nd - setup file sharing on folders (right click )

WEP,WPA, etc is a great ideas but this if for someone who obviously doesn't know how to do it to begin with... kinda a waste of info... shit other things to knock down on unwanted traffic is static ip and limit the number of open ip.