Try out several of the online bike fit calculators and then look for bikes used and new that fit. I think that the last issues of Road Bike Action and Bicycling have some good info for newbies as part of the buyers guides. I agree with some of the others that you should be able to find an entry level bike at a shop in your budget. The LBS is also a good place to ask your questions if you don't have a lot of experience. Ask around and you should be able to find a good shop and then go take a look.