I guess the bike part of triathlons could be an adventure in cycling, so it should be fine to post a quick note of response.
Your budget is definitely enough to get into the "entry level" (the term is not always appropriate, but it's standard) road bikes. There's a lot of competition there, and you pretty much get what you pay for, as long as you stay with major manufacturers that have dealers all over the country and good customer service. That would exclude the brands that are sold by mail-order only and look very appealing in the ads but end up costing you more money and frustration in the long run, especially for a beginner who really needs the support of the shop.
You will find little in the way of differences from one brand to another in the price range. The car equivalent would be like if most small cars in a price range, regardless of brand, were using the same engine, transmission, and other parts. There's probably less difference between bike frames too than there is between car bodies. The question now is, "Who's going to support the product the best?"
The place to start then is not really so much "What bike?" but rather, "What shop will I choose as my home shop?" and then "What do they carry?" Really. It may be more important what shop you choose than what bike brand. Visit various shops in your area and see which seem to be the most knowledgeable and helpful and give you the best feeling. After you land on one, then pick a bike.
