My little brother is on his third tour of duty in Iraq, and everytime he leaves I fear it will be the last time I ever see him, so I do understand your fear.
The Navy is actually a pretty good idea, they probably aren't on the front lines in Iraq. My sister joined the navy to help pay for nursing school and it worked out well for her.

It is so hard when people we love do things we don't want them to do- we feel so helpless. All you can do is BE A GOOD EXAMPLE for your brother- that speaks volumes!
He's very lucky to have a brother like you to guide him!