A camera itself cannot be professional, as the camera is incapable of making money.
The photographer, however, is. Any SLR (Digital or otherwise) can be used by a pro to great results (I know some people will tell me that ANY camera can be used, but it's very rare to take an awesome shot on a P&S, but it has been done). Some will recommend Nikon, some will recommend Canon, some will say film, others will say digital, but in the end, it doesn't matter about the camera itself.
It's all in the lens.
I've seen amazing shots come out of the Nikon D40, and I've seen cringe-worthy shots come from the Nikon D3.
However, as you are one of my fellow teens, I'm guessing you don't have a huge budget. I'm going to suggest you get any of the following:
Nikon D40 (I hesitate to mention this one, as it is the most basic dSLR on the market, and can only autofocus with certain lenses)
Nikon D60 (I hesitate to mention this one, as it is the second most basic dSLR on the market, and can only autofocus with certain lenses)
Nikon D80
Nikon D90
Canon 1000D (I think this one was the... XSi in North America)
Canon 400D (Known as the XTi in North America)
Canon 450D (If I remember right, it's the "XS" to you guys in the U.S)
Canon 40D
Canon 50D
Pentax K100D
Pentax K-m
All of these can do black and white, colour, all can do portraits, street candids, nature, you name it.
As for the zoom, each of these systems has many lenses available. Wide angles, zooms, fixed focal lengths, and each system's lenses has professional quality "glass" available.
Personally, I use a Canon 400D with a 16-35mm L lens, but I'm no pro.