In the section "Latest IT News" I mentioned that Amazon.com has opened up a web service where applications can query the service(information about goods), and the service spits back an XML file of whatever they queried. So you can have a form on your web site where the user can search for an item from Amazon.com. After the user submits, you can program your script to query an XML file from the Amazon Web Service according to the values submitted by the form. To get a better understanding, I suggest checking out:
Jeff Houser explains it very well.