I don't know if you have got your product listing sorted out, but I figured that I'd reply with how I set mine up.
Assuming you have your shopping feed set up correctly (attributes like 'product type', 'brand', 'condition' etc) which it sounds like you probably do, you need to enable a couple things in adwords.
*Make sure you have 'Product Extensions' enabled/added in the AD Extensions tab*
First I select the 'auto targets' tab. Hit the 'Add Product Target' tab.
In the dialog window, select the adgroup you want to apply this to.
Then I select 'Add a group of products'. A dropdown containing the attributes will then be available.
I choose 'brand' because that works for my strategy. Then enter the brand name you have listed (or whatever attribute that corresponds) in your shopping feed.
Click 'verify' for any possible spelling issues or whatever then Save.
The next step I do is to go to the ADs tab and Hit 'Create new AD' and select 'Product Listing AD'. Small text box will appear that you can enter a little promotional blurb like "Free shipping!" (or whatever)- It's not necessary to fill this out, but I think it's kind of nice. Then hit save.
Rince and repeat for any remaining adgroups.
Hope that helped