Use a computer that is plugged into the router with an ethernet cable.
Open internet explorer.. in the address bar type in 192.168.1.1 and hit go. You'll be prompted for a username and a password. Leave the username blank, and for the password type in admin
There should be a link on this page that says Wireless. Click on that and enter a name in the box where it says network name/SSID. The name you enter here will be what your network shows up as when you look for it. Hit the Save Settings button at the bottom.
Then click on the link at the top that says Wireless Security. For the security type, the easiest choice is WEP. After choosing that, there will be a drop down menu that wants to know whether you want 64 bit or 128 bit. 64 bit means you will use a 10 character key, and 128 bit means you will use a 26 character key. For ease of use, you can use a 64 bit key, then where it says Key 1 you can just enter in any 10 character password that you like, hit save settings at the bottom and you're done.
There are a lot of other features that you can get into for security, but that's the most simplistic setup. Check the Linksys website or call their tech support (800) 326-7114 if you need more help :)How do i properly secure a wireless network?
the linksys website might tell you
http://www.linksys.com/servlet/Satellite
the info is near the bottom under their advertisements
good luck