From your initial post, it sounds as though you may be confused as to where the belt is supposed to go. The "waist" strap of the pack is not a waist strap, it's a hip belt. Its function is to transfer the pack's weight to your hips, where your body can most easily carry it. For me, the belly button level is just about right, but I'm female.

Feel your sides below your waist to find the top of your iliac crest--the top of your pelvic girdle/hip bones. That is where the pack's hip belt should rest. Level with the top of the pelvic girdle, on your backbone, is the bottom end of the torso measurement. As Lori mentioned earlier, the top end of your torso measurement is that bump on the back of your neck.

Get someone else to do the measurement for you. Every time I've tried to do it myself, I come out with a different number! It's pretty hard to do alone, since none of us have eyes in the backs of our heads and few of us are contortionists!

If possible, find a store that specializes in backpacking gear (like REI, EMS or a local store), find an experienced clerk (not always easy!) and try on a bunch of packs until you find one that is comfortable for you. It's best to box up your gear and take it with you, because the pack needs to fit three ways: It needs to fit your body, it needs to fit your gear and it needs to be comfortable for you to carry around with the gear in it. Pack fit is almost as individual as shoe fit, so be persistent! Even if you don't buy one of the packs you try, at least you'll know how a comfortable, properly-fitting pack should feel. Try to go when the store is not crowded, or, better, make an appointment with their most experienced clerk at fitting backpacks.

Have you read the helpful articles on the home page of this site, left-hand column?

Good luck!