Fixed gear bikes belong in one place. The track. Not out in traffic on the road. I know may people who ride them. I have no such ego. There are other ways to learn correct techniques that are much safer.
This is honestly the worst road bike advice I've ever heard even after 14 years of working in the bike industry.
I disagree with this. I commute on my bike to work 80% or more of the time. In all weather, all year long. The majority of the time I ride a fixed gear. It's fine in traffic once you learn the quirks. It is a poor place to start as a beginning roadie. Otherwise, it's remarkably thereputic.
Over the last 25 years of my cycling life, I have ridden just about everything. Steel, titanium, carbon fiber, aluminum. If I were still racing, I would say get a carbon fiber Trek and go at it. They are light, strong, comfortable, and disposable.
Kestrals are weak in the bottom bracket area and I have seen several fail. Especially those old ones. Avoid.
If you are buying a bike to ride and train and basically learn the roadie way, the advice about buying an old steel frame is excellent. There are great frames out there just moldering away. Go into an old school bike shop and they will usually have some for sale on consignment. My fixed gear is an old Paramount, (a 50th edition for you bike nuts). There are tons of nice frames out there, but look for frames with racing geometry by an established maker. Then add a modern component group (Dura Ace is the best shifting-despite what the Campy lovers will try and tell you). The real deal on steel is the road feel. Nothing, not even titanium, feels as good going down the road. It has a springy, resiliant, comfortable stable feel that is unique. You should be able to build a bike like this around 22 pounds which is fine for road riding and training. Look for a frame in your size, made from a good tube set like Reynolds or Columbus. Look for a frame with horizontal drop outs so you can make it a fixed gear in a few years.
Titanium is also an excellent frame material, but much more expensive. A 10 year old Litespeed would be a good choice, again outfitted with the component group of your choice, but I am very partial to Dura Ace! It will easily cost twice the price of a good used steel frame though.
As Cary mentioned, the only thing that really matters for a non-racer, is fit. Let me add to that, a good saddle is nice as well. You may go through several saddles to find one you like and can live with. My favorite is still a San Marco Rolls which has been made the same way for 20 years! The newer phiziks (sp?) fit me pretty well also.
One last thing to look at is frame geometry. I would err on the side of stable, as opposed to twichy--a bike shop can guide you here. You'll understand why the first time you wail down a long hill at 50mph.
BTW-resetting the rear drop out width on a steel bike is no big deal. A custom shop can cold set it for you easily. Do not do this with aluminum or CF. I don't know if it's possible with Titanium.
I did not mention Aluminum bikes. I don't like them. The road feel is dead. They are cheap and light, but again, I would put these in the disposable category. Fine for a racer for a season or two.
One last thing. Don't get too hung up on weight, at least not yet. COncentrate on fit and quality. Get decent components. Ride a lot. In a year, things will be much clearer to you.