Hey!
Basically, the CCNA tests your knowledge of TCP/IP networking and beginner CISCO router configuration.
I passed mine in January, after two weeks of INTENSE study, and found that it really helped me get a grip on the Layered Model, TCP/IP, basic routing and basic Cisco configs.
You will also need to learn some basic industry specs on other protocols and WAN technologies, how to config some other protocols on Cisco, such as RIP, RIP for IP and IPX/SPX, basic bridging concepts, router diags and troubleshooting, etc...
In the IS biz, if you have a CCNA or higher you are considered more networking savy than someone with just a CNE or a MSCE.
If you are going for it, find out the latest test number, then get either the CISCO books or a good hard-cover CYBEX book. Also, try to get the Cisco Sim software, unless you have a router you can experiment on. I would VPN into work and experiment on a Cisco 1600 I set up for a users home office!
Good Luck!