There are many ways to create a vignette.
One way would be to use the circle marque (selection) tool. Add a new layer and drag out a round shaped selection, then feather the selection with a fairly high setting. Fill the layer with the color you want your vignette.
Or you could use the gradient tool and choose a radial vignette, then play with the settings to see what you get.
I'm not sure if version 7.0 has it, but later versions actually have a vignette feature, I think it's under lens corrections.
Personally, I always liked to be more creative than just having a round vignette...so I would use the burn tool and darken the edges and whatever else, to get the result that I wanted. (always on a separate layer of course)