I have an Linksys router that is a few years old

You can download the manual for your router from Linksys. You don't need the CD to setup your router in any way at all.
Once you have read and understand the manual just access the routers setup page by typing 192.168.1.1 into Internet Explorer just like you type in a website address, a small GUI window will popup asking for your username and password, as long as your routers password has not been changed the username and password for Linksys routers is usually Admin for both.
Make sure you set your wireless up securely by using WPA encryption, it's all in the instruction manual and very simple. Linksys also has a live chat support on their site which is very helpfull.
Here is a link to the Linksys support page, just put in the model number of your router and it will take you straight to the download page:
http://www.linksysbycisco.com/LATAM/en/support