JimmyJohn, a buddy of mine and I tried to hike the AT not too long ago. My trip was cut short after a bear decided to run off with my boots and my knee giving out (going down hill is harder that up!). Anyhow, my advice is echos everyone else. Test your pack.

If I were you, head over with your pack loaded to REI. The folks there see many thru-hikers and they can give you some VERY good advice: from how the pack should fit to whether or not you really need those books you think you will read on the trip. They (in my experience) will bend over backwards to make sure your pack is setup right even if you didn't purchase it there. March is almost here and I bet there will be tons of thru-hikers there. Talk to them some have done it more than once and know a thing or two and aren't typically shy about giving you their 2 cents.

Once you have your stuff the way you think you want it, take your bag loaded and hike for 5-7 miles in terrain similar to what you expect to encounter. Make sure you have the same amount of food and water (heavy) that you expect to carry. I typically aim to have my pack to 25lbs. without food or water. Once grub is added it's about 30-35lbs (1 week's worth).

Oh I almost forgot if you don't feel comfortable taking all your bag fully loaded into REI just take the bag and ask if someone can help you adjust it. They have sand bags that they can put in it to simulate the weight. Oh and have fun! Some of the nicest people I met were in GA. Talk about southern hospitality!

-Humby