Hi,
I have been in data networking for many years and amongst others have worked for two major isp's on core mpls and ip networks. My recommendation to anyone attemping a career in this field is to first learn about networking before trying to pass CCNA.
The CCNA exam is based on alot of dated/legacy technology and only really skims the surface of real ip networking. CCNA does little to explain the proper workings of ip networks and does more to confuse a novice than actually teach them what they need to know.
You should definately aim to pass this exam and further to CCNP or CCIE, but take it from me you'd be better reading industry recognised material which will help you understand internetworking more accurately and then go back and conquer the b**ch that is CCNA.
Here are some recommendations....
Buy the following books and read them cover to cover -
Internetworking with TCP/IP, 3rd Edition
TCP/IP Illustarated
Internet Routing Architetures, 2nd Edition
CCIE Professional Development - Cisco LAN Switching
CCIE Professional Development - Routing TCP/IP Volume I, 2nd Edition
Buy yourself a Cisco 837 DSL router, learn how to configure and connect it to your DSL internet connection (£100 on ebay)
Buy yourself a few Cisco 2610's and learn how to configure protocols properly (£75 each on ebay)
There is no substitute for the real hardware, all of the simulators I have ever come across are a load of crap. Without debugging what is the point? (with the exception of Dynamips which offers a Cisco kernel and allows you to load actual Cisco code onto the the sim).
Another recommendation is CBT Nuggets courses. They are computer based and cost around £40 per cert. The guy that delivers the courses is second to none and makes everything so easy to understand.
I hope this helps in your quest. Understanding is the art, without that you will lose direction very quickly.
Drop me an email with any questions. I really think you'd get more out of a CBT Nuggets CD and some cheap home lab kit than sims or expensive courses!
Cheers.