Gimp techniques

im trying to soften the edge of circle using gimp, i can obviously use the smudge tool however this does not create an even effect, thus keeping the circle looking round.... does anyone know how to achieve this

You could try some of the tools under Filters > Blur. They were able to nicely soften a circle I drew. The disadvantage to using them, however, is that they affect the entire image. I'm not sure if you can limit them to a specific area, though. In the worst case scenario, you could just cut a piece of the image out, filter it, and paste it back in.

As you can probably tell, I'm no expert on the GIMP, so I suggest looking here rather than listening to me :
http://gimp.org/docs.html

You can select an area to perform most effects on, including the blurs. If you want a nice clean selection, use the magic wand to select the circle, then go to edit->grow selection (or something like that), and pick the size you want. This will also select anything near the circle, but that's solvable (just a little more complex to 'splain).