Tim, in my mind you would be doing a mistake by dropping out of High School. Even if most of what your learning in class is totally pointless, while you're at school you're getting older, acquiring maturity and interpersonal skills.
I know it's not easy to find the motivation required to study hard everyday, but it's your job to find a way to motivate yourself and get thru it.
Ask yourself why did so many people you don't know took 15-20 minutes (large messages) to answer YOUR topic... It's because they STRONGLY believe it will be better for your military career and your life to complete H.S.
I guess i know how you feel tho. I've been willing to drop out since my first year in CEGEP (I'm from Quebec). For the past 5 years, i had to motivate myself and study the best I can even if I was bored... Now I'll be getting my bachelor degree in public relations in April 2009. I'm in the process of joining the Forces (waiting to be sworned in) as an Infantry Officer. I couldn't have done that if I dropped out 5 years ago.
Join the reserve, train very hard, both body and mind. If you can't kick your ass hard enough to complete high school, you'll have a hard time in the army... If you get through the recruiting process.. You may find out soon enough that if we strongly suggest you to complete H.S., it's nothing compared to how STRONGLY the military career counselor will URGE you to finish it before joining.
P.S.: If for any reason you HAVE to drop out, join the army that take your free time to travel around the world and all that stuff.
P.S.2: Sorry for the mistakes in my post, I'm doing my best but I'm just a "frenchy" after all