Changing careers, need some advice pls

Right now I'm a network admin for a midsize company. It was great at first, but now its turned into nothing more than babysitting. I'm not really learning or doing anything new and exciting. I was looking into getting into the security field.
Right now I have pretty much zero *nix experience, so I should probably crack open a book, and start messing around right? There are already quite a few books that I'd like to look into in regards to security and such, but I'd like some advice from those that are already in the field.
What areas should I focus on in the beginning?

Another question that I've been wondering about too...
As far as OS's go, what is the prevailing one that security apps are run on? I know a lot of you are *nix fans and everything, but would someone who runs security apps on Windows be laughed out of the office?
What do you think?

Thanks for any advice or answers!

Sounds pretty much like what I did up to about a week ago. Anyway I'm headed back to a public service job I left 7 years ago. Pretty good area mixed of Unix, Linux, Win, Novell you name it it's there. Lots of peers also to throw around ideas and a perfect place to take classes for free. Pay just a bit less but public service is pretty stable unlike the private sector right now. Hope this helps