One thing that nobody has mentioned yet is the importance of a good fitting, especially for a new rider. A road bike is going to have a much different feel than the more upright position of a mountain bike or cruiser. Considering that you are new to the more streched out position you won't really know at first if something is uncofortable because its a new position, or if something if wrong mechanically. Where ever you end up buying a bike make sure they have employees who are competent bike fitters. Preferably somewhere that allows you to go back for at least one refitting. This will allow you to start more upright and gradually strech out into a more aerodynamic position. Be sure to ask what the policy is at the store you purchase from.

Some shops even allow you to come back for unlimited free fittings for a year. B&L does this, and I believe Nytro does as well.