For jewelry, you should probably be buying a skybox.
A good camera will help, but a skybox will really make shit look good.
edit: sorry, maybe skybox is not the right term.
Something like this:
will let you have diffuse light and a seamless backdrop.
A lot cheaper/more compact than getting actual soft box lights and setting up a seamless background and all that. They even make some that are like those pop up laundry hampers...just put some bright lights outside, put the item inside, and shoot away.