While I normally agree with what John writes, I disagree with him in this instance. Go ahead and start riding until you're comfortable doing 5-10 miles at a lick, and then go shopping. It seems to me that, if you're going to spend $500-1,500 on a touring bike, it doesn't make sense to start by spending $500-1,500 on a different road bike. My take on it is to go ahead and find that touring bike -- it's a special kind of road bike, and you can start getting ready for a tour by riding it now.
I agree with looking at the AC buyer's guide. Most (if not all all) touring bicycles will work. Then check manufacturers' web sites, locate the nearest dealers, and start calling around. They may be hard to find, so unless you live where bike touring is popular, you may be in for a long search.
If at all possible, try two or three different models before you pick one. You're looking for a bike that feels right. Sounds nebulous, and it may be, but when you find the right bike, you'll know it. Don't buy it if it doesn't feel quite right. I'd want the dealer to swap stems to get a good fit, and double-check the wheels for tension and true (tension is often inadequate on machine-built wheels). Given your weight, you may want to get the bars set about even with the saddle -- don't leave the shop with the bike if your thighs are hitting your stomach when you're pedaling! Check out a gear calculator like sheldonbrown.com/gears -- I'd say you should accept low gear of no more than 25", with 20" preferred, if you're ever going to tour in hills or mountains.
If you can't find a bike shop carrying a touring bike within a reasonable distance, you may have to order one. Most LBSs can get the Surly LHT. Since it's just March, other dealers should be able to get their favorite brand of touring bike for you. Make sure you and the dealer understand you're not going to pay for a touring bike that doesn't fit you (see above). Pick one, cross your fingers, order it, wait for it to come in, then have fun!
