I have just a little bit of experience in this (not sure of details). My son's about to join the Air Force. He visited all the different branches - some had more requirements (physical, test scores, no tatoos, etc) than others. We got a lot of information off of about.com under the different military branches. Or you can just go to each branches' websites. I believe they have the physical requirements (what you have to pass and be able to do in basic training) listed in detail, or what kind of meds you can / can't be on. Plus, you have a "brief medical exam" when you take that initial test (the ASVAB).
I just found my son's packet... let's see. Besides drug and alcohol testing, and a physical and neeing to be able to lift 40 lbs, it says "you will take a very sensitive hearing test." It doesn't say that you have to have 100% hearing. (and, this is for USAF only - not sure about the other branches).
Thank you for wanting to serve - I hope it works out for you.
Keri