Ask HN: What's a good way to get into a network security career?

I'm a software engineer working for a consulting company. I haven't done any real programming at work in over a year and a half now because my current client has me doing IT and SharePoint Administration work instead. So I'm thinking about a career change that my current work experience can help me with.

I've been thinking of getting in to the security side of IT. My background is pretty technical. Besides programming experience, I know the basics of networking, some hardware, and in my current work I'm managing an active directory, some Windows Server machines, a couple SQL boxes, and SharePoint.

So for someone with a little bit of IT background, where would you start? Going back to school isn't really an option right now. Though, I'm open to the idea of getting a cert or two if they'd help. Any good resources to help make this transition happen would be very much appreciated.