Sponsored Links in Meta Search Engines

Meta search engines like dogpile list the sponsored links between the results (it is claimed as paid-for links). In fact they search within Ads by Google or Ads by Yahoo.

I want to know how they do this. In other other words I'm curious to know the technical issues about the script.

It has to be somewhat similar to adsense which offers targetted ads. But as one has to be familiar with the meta search engines to really make a studied comment on the type of script. However it would not be difficult considering , it is a search engine!