I hiked the Appalachian Trail in '04! Also the Ice Age Trail in '03, the Pacific Crest Trail in '06, and I just finished the Continental Divide Trail this year. Yeah, it gets pretty addictive! I'll probably be out on the PCT again next year if I can save up enough money. Fucking jobs! Work to hike...
There is a shit ton of info out there. Like Loess said, Whiteblaze.net is a good place to start. They have forums to read and planning guides. Baltimore Jack has an especially good piece about resuppy strategies.
As far as gear goes, check out places like backpackinglight.com and Ray Jardine's website. You can make a ton of your own stuff, from quilts to stoves, and save a lot of money while still carrying lightweight gear.
I would also suggest you read up on
http://www.trailjournals.com and see what other people experienced out there on the AT. This will help you plan, and you can learn from their experiences. Hell, I even did a journal there this year for the Continental Divide Trail! The ramblings of a drunken derelict, indeed.
If you have specific questions that you can't find answers to at these places, feel free to contact me and I'll happily barf up more info than you could possibly want. I love this shit, and love talking about it. Hiker Trash!!!!!!