The former reply is right, you need to talk to a recruiter ASAP as it may take some time and you may have to back door into the military nursing at this time. Army nurse corps right now is basically be ROTC and in school for nursing, get an Army scholarship or serve 1 year in the guard/reserves then go active duty. I am assuming the AF is in a similar situation. As for the physical training.....can you run, do sit ups and pull-ups? I am former AF enlisted and I am told by the Army nursing officer I know that physical training for nursing is much less vigorous than basic training. You have to think, you will be an officer and things are different for officers. That said, it's always good to be able to run for 30 minutes straight. Talk to a recruiter, but take everything they say with a grain of salt.
On a side note, good choice! GO AIRFORCE!