At $600 I would choose the Nikon D3100. Shoots in 1080p and has just about everything you could ask for in an DSLR. Either that or the Canon EOS Rebel T3. Both really good starter camera's. I prefer the Nikon camera layouts, a little more than the Canon's. The kit lens that come with both of these camera's are pretty good, much better than the Sony's. You also have far more lens choices if you stick with Nikon or Canon when your ready for specialty lenses.
A good lens makes taking great pictures
easier, but only if you know how the camera works. If you want better quality pictures, you gotta read up on fundamental techniques of photography. It would be a waste if you purchased a fancy DSLR just to leave it on "Auto."
The Sony is a gizmos and gadget camera. Too big to be a point and shoot and not nearly as good as a DSLR. Its basically a point and shoot on steriods. I'd pass on this. If you want a point and shoot with manual controls, much like a DSLR, take a look at these:
Panasonic DMC LX5K
Nikon P7000
Powershot G12
I would suggest going to a real camera shop and ask a lot of questions. Get a feel for which one your really comfortable with. Don't be intimidated, we were all noobs at one point.
The Nikon and Canon DSLR's also shoot phenomenal HD video's, but sound quality with the built in mic is not all that great (common with
almost all cameras that are not dedicated for video).