If you haven't already found them, there are lots of excellent articles on gear selection listed in the left-hand column of
http://www.backpacking.net/, the home page of this site. It's a good place to start for ideas on pack-fitting and selection, including how to measure that all-important torso length. Note--get someone else to measure your torso length for you; when I tried to do it myself I had up to 2 inches difference each time I tried! Please note that it's best to get the pack last, after you've acquired your other gear. That way you know your pack's volume will fit the gear you want to put into it and that the pack's suspension will support the weight you'll end up carrying.
Since we're all built differently, pack fit is almost as individual as shoe fit. After you've bought a pack, load it up with your gear and the equivalent in weight/volume of several days food and hike several hours around the house (or around the neighborhood in good weather), taking care to keep the pack clean so you can return it if it doesn't work for you.
Another good site for gear selection is
Mark Verber's website. Lots of ideas for gear, from the latest technology to low-budget alternatives.