You can sign up for Adsense at http://adsense.google.com - I'm not quite sure about the Ebaying/E-buying deal.
While this has nothing to do with Google Adsense I'm assuming you are trying to figure out what the new ebay contextual advertising program is. That program is called Ebay Adcontext and can be found here: http://affiliates.ebay.com/ads/adcontext/ I have not heard if anyone is a current beta tester or not? It does sound like a great program tho. I know I buy so much crud(cleaned up for public post) off ebay it aint funny.
I signed up for the Beta program, just got an email from them saying they are reviewing apps and will most likely accept more Beta testers than originally planned. Whoot!
i did not get any email about it but i wish iget it... at this moment i stuck with affiliate url. I can not figure out how it should look like for developer program (i want to use ebay API)... I did all these steps http://developer.ebay.com/programs/affiliates/affiliateapiguide All works. But how to apply an affiliate url? Any suggestions? thanks