Any bike you start out with will probably be just fine. At that price range they will be pretty comparable in components and performance. Trek has a great reputation and following. My DH has 2 (a mtn and a road) and loves both. I myself have a Bianchi. The brand name is purely personal preference.....

Above all else make sure your LBS fits you to the bike you end up buying. Read up on bike fitting on the web so you know you are getting the proper treatment. My first fit was no where near as in depth as my second fit and I could definately tell the difference. (My first bike was a Giant; it was a little oversized for me). And in the event you have any discomfort or pain from the fit, or even if anything feels a little "off", go back to your LBS for a consult or adjustment. These little details will make a huge difference in your sticking with cycling.....

Then of course, there will be the dreaded SADDLE issue........