Feathering problems

I am trying to vignette a posterised photo so that the edge of the pic gradually bleeds off into white. Ive made a new layer and used 100 pixel feathering. The only problem is that the feathered edge shows distinct banding lines particulasrly in smooth areas such as sky.
I considered trying gradient but as I see it , gradients cannot be applied to an oval vignette . I also tried applying gausian blur to the new layer (ie vinette) but that didnt help. I ca n be contacted via Yahoo Messenger if required.

you'll get a better result using a layermask to produce the vignette.

just draw your oval selection and click the "create layer mask" button at the bottom of the layers pallet.

then you can blur the mask to get the smooth transition.

My ps7 doesnt show"create layer mask". Ive got "create new layer", "Add a mask", and "Add a layer style".
Which do I use ?
What strength blur do you suggest ?

Thanks,
Tried all sorts of methods. The methods quoted in text books dont produce the quality I expect in my work. I was hoping to contact someone who had experienced this banding problem and solved it.
It appears , after days of research,that Adobe are aware of this problem and that PS 7 is NOT capable of prodcing gradients to the standard desired by pro photogs. Their
solutions suggest 'hiding' the fault by adding noise or textures. I dont like bodging. !
Look what happened when they did a bodge on the Shuttle

well, if all you're after is a fade-to-white feathered edge, why not put a layer above the pic and paint in the fade using an soft edge airbrush and white paint? either totally, or to touch up the banding prob you're getting?

Why buy a dog and bark yourself ?I thought computers were supposed to do the work !

Apart from which, I work on 50 pics a week, at 5mins per pic thats an extra half a days work to be paid for by clients, works out at £4 per pic..

Hiding banding has been going on long before photoshop. I've been printing for a very long time, and I can tell you, we were finghting banding problems in printing long before Photoshop had its claws in the process.

Like I said above create the vignette with a layer mask, sinker with the guassian blure on that mask untill you like it. The add a little noise (uniform monocrome unchecked) and thats about all you can do on the quick side.

BT and I posted some stuff on banding a whil back, it is a little more informative. >>>> here <<<<

I have to assume the banding you're experiencing comes from using a gradient. I would never consider using a gradient to make a vignette. I tend to think your best bet is to use tornupinside's first suggestion of using a layer mask with gaussian blur.