I was in the Army for over 6 years. The P.T. test at the time (got out in 02) consisted of push ups, sit ups, and 2 mile run. Most people who had a hard time passing, you need at least a 180 on their scale, had problems on the run. I believe the lowest score for passing was 15 minutes and some seconds. The next hardest was situps. On th P.T. test you had to do as many possible push ups in 2 minutes and then as many possible situps in 2 minutes. 42 was passing for push ups and situps I think was 63. I am not sure now though. My advice, for just trying to get in shape to go, is stretch a few times a day. I mean a nice full body stretch 2 to 3 times a day and then push ups, sit ups, and run. Start getting used to water if you dont like it now because they will make you drink until you puke. Start standing all the time. If you get used to it now it wont be as bad when you have to there. It sounds dumb but if your not used to it, it can be a pain. Oh and practice not putting your hands in your pockets. Your BDUs have pockets but the Army doesnt want you to use them. Some of this stuff is off subject, but its advice that can save you from getting smoked. (Smoked = exercised until thinking death is preferable)
Any more questions feel free to ask.