I'm a Linux (UNIX/Solaris) sysadmin (i.e. if it's broke or we want it built, we'll ask the "sysadmin") who also does Windows and basic ethernet networking.
I broke into the field because I love working with the technology: building my own Microsoft-based computer systems, building others' systems, learning Linux to use remote servers and services, then setting up Linux servers to provide email, DNS, web, etc.
If you don't love getting your mitts dirty with tons of ever-changing technical details of computer system hardware and software, you'll eventually go mad. If you do love it, just find a task you personally want done, browse around for software which will do the job if you can't write your own yet (or just write your own), and repeat until you can explain what you've done over the years to a layman/interviewer. Start at the bottom, work your way up.
Experience was key in my case, with most of that which got the ball rolling being from my own hobbies. I have not completed any college degrees; most of the classes I took were unrelated to IT and those that were were antiquated and unhelpful save the one regarding C++ programming.