If you are interested in Networking,then you have chosen the correct certification as a starter CCNA is the course to start for network noobs. But I am afraid the course content and the exam patern is going to change from November 2007.
So start preparing and write it asap.
The method I adopted for completing my MCSE in Windows Server 2003 is go throught the entire MOC.
Finally completed all my 7 papers after doing practicals in my training centre
The certification is valid for 3 years.
Before its expiry, you have to write the next level of certification namely CCSP or CCNP depending on your specialization.