Have you looked into Shopping.com's widgets? I've done a little work on building a parser for their XML feed for a client but haven't seen the widgets library they are now providing. The feature you are asking for might just be in there.
If not, then its a fairly straight forward process to send a sample feed to someone and describe how you want it parsed. The API will let them break out the pieces and decide what part will go into your banner. Then you can use some of their default xsl transforms that you can get from the partner site, or have a web designer create their own.
So if you have pages that display products now, all you need to do is create a couple new php functions or a simple class that would build the banner and either apply an xslt template or process the raw XML data into html.
I don't have access so I can't be any more specific at this point as to what is available.