Well, since I'm the one who's up I'll shoot from the hip here and try to answersome of your questions even though I'm a squid.
The Army Reserve is exactly what the name implies. It is a unit of the Army that is kept in reserve status. It draws it's enlisted from the area local to where the unit is based out of. They still classify as weekend warriors in the effect that they drill one weekend out of every month and then two weeks in the summer. In theory they are more likely to be deployed than a National Guard unit.
The Army National Guard is basically the same idea, but with one key difference. The National Guard dates back to the idea of the Militia. They actually belong to the state where they are located. Thus the reason they used to be called the Hawaii National Guard, Illinois National Guard, etc. In theory their primary job is the defense of their state. Because of this the Governor of the State issues their marching orders. In the National Guard you are likely to see jobs such as mobilization following a natural disaster to keep order, enforce curfews... generally backing up the police. However, times have changed. Since the end of the cold war and the reduction in Defense spending the US has become much more dependent on its national guard units. They are commonly deployed in the event of war now. It is much cheaper to maintain and operate both guard and reserve units because you don't have to pay for their room/board/etc.
The Air National Guard is the same concept. Defends the skies of the state. But, are also commonly deployed. However, I believe you have to serve a minimum time as active duty air force before you can join the air guard. I could be wrong about that though.
Air Force and Navy reserve both require you to have been active duty prior to becoming a reservist. This is mainly because many of the jobs are so technical the service members need to have worked in the job for years or their would be no point. I know I couldn't do my job if I was only given training once a month and two weeks in the summer.
As for college. Don't get terms confused here. ROTC is Recruit Officer Training Command or some such thing. It is where you go to college paid for 100% by the government. Then when you get out you are obligated to go serve as an officer in the military for, I believe, six years. Oh and we don't give much respect to ROTC brats. Academy Grads like Chris (8k) are completly different. They did their dirt.
Now, what I think you are thinking of is the GI Bill. You enlist say for instance the Army Reserve. For the first 12 mos. your in you pay like $100 out of your Army paycheck to the GI Bill. After that you get like $52,000 for college (so long as you are enrolled in like 8 semester hours or something). Actually, I think it might be up to like $60,000 for college.
It's a pretty good deal. But keep in mind this. Even if it is $60,000 that isn't necessarily going to pay for all of your college. (But, it's a hell of a big help.) You are also limited to what Universities you can use it at. Mostly, state universities. But the biggie, is your ass is not yours anymore. It's Govt. property. THat means you are limited as to where you can get a tattoo, how long your hair can be, you can't grow a beard (but that's not really true), etc. What it really means though is that you're half way through a semester and life is good and all of the sudden the Pentagon says activate that reserve unit in Hawaii. Bye, bye. You drop all of your classes and you deploy. No arguments or nothing.
Not trying to scare you off or anything. Just telling it how it is. It is a good deal, but it comes with sacrafices.
