DITTO the advice about getting in shape BEFORE you join. Don't just lose the weight but build up your stamina too. There is LOTS and LOTS of heavy marching and running in formation with your company.
When I was in boot camp I was young and in shape and it was hard then and I had been doing heavy construction for years when I joined.
There were days when the company commander seemed like he woke up on the wrong side of the bed and we got to do pushups out in the hot sun all afternoon! Besides the marching and walking we had to do a LOT of swimming too because if you are going to be on a ship it might sink one day and you HAVE to know how to not only swim but stay afloat.
I remember towards the end we were thrown in a pool and we were told we had to tread water and stay afloat for 20 minutes without touching the sides or bottom. MAN I about died! LOL! I was STRUGGLING the only thing sticking out of the water was my nose I almost drowned! LOL!
Also the very last thing I had to do (we ALL had to do it) was run in formation as a company for 3 miles. This is a lot harder than it seems because you can't run at YOUR pace you HAVE to keep up with the company.
When I was in if you couldn't do this they wouldn't let you pass Boot Camp and you had to start out all over again in another company. If you failed again they would send you home.
I don't mean to scare you. MOST people make it through. Lose the weight and build your wind up and you can make it.
And as the other poster said what is working for me is counting calories and attending Weight Watchers, I am doing both and also I take Alli. So far I am losing!
good luck!