any module that allows users to create ads, and other users to publish them on their site?

I want a portal where users can create ads, similar to google adwords.
Then other users can put other users ads on their site, similar to adsense.

I know there are a few ad modules that allow users to uploads adverts to my site through CCK, is there any modules that intergrate ubercart/ecommerce automatically? is not I could proably configure that myself.

But how do I get the publishers (the adsense side of things) to work?
How can users specify what sort of adverts they want to display and get a code to put on theris site to display the adverts?

Does anybody have any suggestions for this?

Thanks