Hi,
the basic idea is simple. Get a frame. Throw some parts on it.
There are several companies that will sell you a complete tourer.
The tricky points... fit is crucial. and it can be hard to find one to test ride. There are actually different types of touring. I do lite touring, and any bike that can fit a rack has the potential to do that. A comfy seating position helps. Then there is loaded touring,
and expedition touring. The Surly LHT and Trek 520 are very popular. There is a bike made in Toronto called the Urbanite that really ought to get more attention. I just got a Gunnar Sport, I'm going to pick it up manana. I'm a huge fan of Waterford (Gunnar is a subsidiary). Waterford makes a great expedition tourer, and of course the Sport which makes a great lite tourer. Cannondale makes a tourer, but I've never tried one. If I was rich, I'd have a custom tourer made from titanium. That sounds cool. Other than that, you mostly need to pick some low gearing, a comfy seat, and some good tires. WHile the Schwalbe Marathon and Conti Top Touring get all the buzz,almost any tire around 500 +/- grams is going to be very durable. Just remember, ruggedness adds weight, and the more rugged the bike gets, the slower it feels.