I need some pages (specific URLs) to only show one sponsor's ads. How do I do this?
You can do that with Page Targeting. See the below "recipe" in the AdPlugg Cookbook:
I'd probably recommend doing it with Placements. Create a Placement that uses Page Targeting to target that particular page and then create a second Placement that uses Page Targeting to exclude that particular page. Then target your ads to the two Placements based on where you want the ads to appear.