Methods:

I used to be in a position very similar to yours, and the best advice I could give you is: "Read!" I know it may seem boring, but reading and truly understanding the underlying concepts in the TCP/IP protocol, and other networking concepts such as routing, switching, and OS interaction will greatly improve your ability to demonstrate your knowledge of computer and network security.

Once you've learned the fundamentals of networking and OS operation (and yes, the OS operation part is pretty important because quite a bit of network security relies on host security), then you can get the theories and ideas behind network security in particular.

You may think this is really boring, and that you'll learn more by just fooling around with stuff (which is exactly the way I used to be), but in reality learning only the actual operations severly limits your usefulness as a security professional. If you don't think you'll be able to motivate yourself to read and learn the fundamentals, then maybe you should consider going for some certifications (CCNA, and CISSP jump to mind immediately; perhaps MCSE), that way you'll have a reason to learn the down and dirty stuff, plus you'll have something to show for your effort.

I hope this helped!

Regards,
Wizeman