There are tons of web sites with helpful (and not so helpful info) on sizing a bike. Most can get you into the general ballpark.
Heres one: http://www.wrenchscience.com/WS1/default.asp
I'm 5'-9" and ride a 16" or 18" MTB, 54-56cm road. For me, the top tube length is what defines my fit. You can tweak a too small bike a bit with a longer stem or seatpost.
Best thing to do is work with the shop to find one that fits you and one that you feel comfortable on.
This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.