It seems I've come a little late to this thread, but here's free advice for what it's worth:
-Be sure to get a bike you can ride in a nearly upright position! You're not Lance Armstrong and you don't need to ride like him! Your hands, wrists, arms, shoulders, back and neck will thank you. In general, this means the height of where you grip the handlebars should be two or more inches above the top of the saddle.
-The most important bike fit item is the seat height. If you feel pain or soreness in the front of your knees, raise the seat. If you feel pain or soreness in the back of your knees, lower the seat. When you get near your ideal seat height, small changes in height will make surprizingly large changes in comfort.
-Don't be afraid to get a big fat seat with springs. These are well suited to upright riding. I got one for my wife, added higher handlebars, now she loves her bike.
I've learned this through recent experience, the hard way!