You say "get a security clearance" like its as easy as that. I myself have one, but was fortunate enough to have a technical job in the military that provided one to me. I now work in the DC/MD area where a majority of the jobs require it. If you don't live in an area near a major government facility a clearance won't get you crap.

The military is a good option. It worked for me, but its not for everyone. Starting out as a system administartor and having alot of initiative would also work. Start there, get into networking and just keep learning. 99% of the people in IT security have come up through the lower ranks of IT jobs....