Paint.NET :: Fade Away From Selection For Pretty Icons

I am trying to make pretty icons. These are non regular shapes.

Simple case: I have a red circle

I want to select a band say 6 pixels thick all the way around the circle

Now i need to fade from the inner edge of the selection to the outer edge so that completely transparent

I am left with a red circle that fades out perfectly and will sit over any background.

Firstly how do i make such a selection? effectively what i want to do is select my shape and then make a buffer of it?

Secondly how do i do the fade part?

If see the symbols that get installed by google earth (or any other nice non square/circle symbols) you will know what im trying to achieve.

I can do these kind of fades quite easily for whole images or with gradients for regular shapes but for something like the shape of a person or car it gets more difficult!