One thing to note. You got 600$...some folks may tell you to get one of the hybrid point and shoot with interchangeable lenses. Which are nice. But eventually you are going to want a digital SLR. They cost more, but gives you more options on the lenses and the things you can do with them.
My cousin has a very nice hybrid, and this week he played with mine, and its going to be his next big purchase, a d3000, which is in your price range compared the D5000 I got
One other thing. The camera itself is cheap compared to lenses down the road. I got two lenses for mine, 18mm - 55mm, and 55mm - 200mm. I love the 200mm, because it lets me get close without being close(I have a 9 month old, and turns out a lot of nice pictures). But I plan on buying an even bigger lens down the line so I can get some nice pictures of airplanes coming in on final, the 200mm does fine, especially since its 12mpixels, and you can just crop it, but right now I cannot afford another 1000$ in a bigger lens. Think of it all as a point to start, and the possibilities you can grow into down the line.