The Linksys Wireless - B routers come with WEP.
Go into your router settings from a hard wire connected PC.
Open a broswer window.
Type "http://192.168.1.1" .. then enter
Default username is none.
Default password is "admin".
On my Linksys on the front page is has the WEP Settings.
Make WEP mandatory.
Click WEP Key Setting.
Choose 64 or 128 bit Encryption
Enter Passphrase - This is what the router uses to generate the WEP Keys.
Click Generate.
Write down the WEP Keys. <you will only really need 1 key>
On your wireless computer(s) you will need to setup WEP and enter the key twice.
Done.