Go to Boson.com, they are a training site and you can download an evaluation copy of a product that allows you to emulate a Cisco Router.
Get a good grounding in network theory as well, learn about switching, routing, IP addressing etc.
As an overview Cisco switches are called Catalyst, the higher the number after the more expensive! Hence a Cisco 2950 is low end workgroup access switch, whereas as Cisco 6500 a modular core switch.
Cisco routers again start with low numbers and increment, so a Cisco 827 is an ADSL router and a 12008 is a large core router usedd by ISPs. The boson product will give you a feel for the Cisco command set called IOS (standard on routers and most switches)