LA,
First off - you'll find answers for just about everything you asked on other threads in this forum and on baseops.net's forum.
But, yes you can get hired off the street into the Reserves or the Guard. I'm an example of that. As for guaranteeing a pilot slot via ROTC, the best advice I can give is "don't suck." It's really not difficult to get an 80+ OM score (go to
WantsCheck.Com Military Flight Planning and Cadet Resources for info on that). Then pray to sweet baby, infant Jesus that you don't bust your Medical.
I'll tell ya one way to make contacts. These forums. It's nerdy as hell, but I got one interview thanks to a guy I talked to on this forum, and got the POC at my hiring unit from a guy on another forum.
Aside from that - every time I flew commercially I'd check in the cockpit and chat. Chances are, one of the two are former MIL. Airshows are also good. I carried around a bunch of note cards and would talk to any Reserve or Guard guys that were there. Ask for their number/email, whatever. Be sure to follow up.
Finally: Do not give up. Don't let recruiters feed you bull****. 99% of the time, they have no clue what they're talking about. If this is truly something you want to do, you need to do some research. I probably spent 3 hours a day on all of these forums reading. Now that I've been picked up I'm trying to figure out with all this spare time I have now.... It's 5 o'clock somwhere.
Best of luck. Feel free to PM me if you have any questions that couldn't be answered by sifting through the 69000 threads on these forums.