I guess I'll chip in a few things. For background, I'm an 11B and I've been in the Army for almost two and a half years. On month 14 of a deployment right now.
While you are in the whole recruiting/MEPS stage I would seriously recommend the About.com website on the military
here. I used it heavily when I was looking at joining the Army. It will give you a lot of details on the recruiting process, MOSs, basic training, life in the Army, and so on. Pretty much anything you can think to ask.
I concur with everyone else who has said look at something besides Infantry. Most of the time it's very, very boring. If you like to shoot or whatever, the Army isn't the place for it. Most ranges will consist of you getting up really, really early to draw weapons, being giving a set amount of ammo to go through the range (qualify, familiarization, MOUT range, whatever), and then you are done and you have to sit around and wait for everyone else to finish. All while wearing an IBA (vest), Kevlar, eye protection, gloves, knees pads, and so on. And ranges are pretty rare unless you are in the field or something.
Unless you are at a range you are probably doing something silly. Painting, picking up trash, sweeping the motor pool, organizing a shed, or whatever. Or just sitting around way after 17:00 because no one will send you home.
If that doesn't dissuade you, I don't think 11B/11C is up to you. I chose to go Infantry (silly me) and just got put down as an 11X. No one asked me. We just got told at basic, "You all are 11Bs." It really makes no difference. We had a couple National Guard 11Cs in our platoon and they did exactly the same training as us, except for a week of learning to set up a mortar tube. Here in Iraq, our Mortar Platoon is being used as a regular line platoon. I think the only 11Cs actually shooting mortars are people working for brigade.
Regarding the APFT, I really wouldn't be worried. We had some extremely overweight and out of shape people in our company and they all passed. You will become much more fit during basic and it's extremely hard to fail basic. Trust me. I think we had one guy (out of 200+) fail. And that's because he lipped off to a drill sergeant the last week.
When you are working out the numbers you should be thinking about are 40 pushups, 50 situps, and a 16:36 two mile time. You need 50% during basic, but to graduate and for every APFT after that you need 60%. You might also be scored on the 18-21 year old scale in basic regardless of age, I can't remember. That would add a couple pushups and situps and trim 30 seconds from your run.
The biggest thing to focus on is RUNNING. Esp if you already are set w/ pushups and situps. No one really cares about pushups and situps during PT. I was and still am a noodle arm when it comes to pushups. If you get smoked and can't do the entire upper body work out it's ok. As long as you keep trying, the drill sergeants will pretty much leave you alone. But if you fall out on a run everyone sees you and you will attract a lot more negative attention. Try to be able to do your two mile in under 16:00 and up to four or five miles at maybe a nine minute pace. Running in formation is usually pretty slow.
Two tips on the regular Army, one big, one small. The small one is opt for the G.I. Bill (some people choose not to) and when you get in go talk to your education counselor about the Plus-Up Program. It allows you to pay an extra $600 in to the G.I. Bill Program. In return, you get an extra $150 a month from your G.I. Bill. Which works out to be worth an extra $5400 over the course of you 36 months of benefits. At a nine-to-one return, it's silly not to take advantage of.
The big tip is be prepared for Iraq. No matter what MOS you choose, but esp if you choose a combat arms branch (Infantry, Armor, FA, Engineer). Be prepared to be stuck over here for 15 months, with one two week break, in a country that gets up to the 120s all summer long, wearing 70 pounds of gear, getting blown up by IEDs. They are bringing in more and more stuff, like AC and Internet, but there are still plenty of creature comforts that you will have to do with out. Things are much better if you are non-combat arms stationed on one of the big camps like Victory or Balad or in the IZ. But you still have to deal with occassional mortars and generally being deployed.
I guess I've ranted for long enough. Shoot me a PM if you have other questions.