I was in a similar position a couple of years ago as an MCSE who wanted to expand my networking knowledge and I decided to go for the CCNA. Most of the CCNA relates to networking fundamentals, many of which you will be familiar with already as an MCSE.

However, there is also quite a bit on Cisco's router O/S (IOS) so you will also need to be familiar with the commands required to configure a Cisco router. If you happen to have a spare Cisco router around that you can play with that would be ideal, if not try to get a copy of a program called RouterSim ( http://www.routersim.com/ ) which will help you practice your IOS commands.

You can get more info on the CCNA exam topics here: http://www.cisco.com/warp/public/10/wwtraining/certprog/testing/current_exams/640-801.html.

Hope that helps.