The D700 is a pro level camera but most Digital SLR (DSLR) cameras are pretty good...better than typical point & shoot digital cameras anyway.
There are several 'entry level' DSLR cameras that can be found for less than $1000. I'd start with the Nikon D60 or the Canon Rebel XSi.
Now keep in mind that there is a lot more than just the camera that goes into a photograph. The lens makes a big difference, and I'd guess that if you cousin has a D700, they also have a pretty good lens to shoot with....and good lenses aren't cheap.
Lastly, it's the photographer that really makes a good photo. So if you really want to improve your own photography, you money would be better spent on some books or a class...than just getting a fancy new camera.