The FancyBox example shows two ways to do this...
various1 displays content from a div on the same page
and various3 shows the content from a web page.
If you use the first technique you will need to have the content loaded on your page in a hidden div.
If you want to use the third technique you will need to create a php page that gets the content from the database and returns that - the php page will need to be "source" coded, not created with WB.
http://www.thenorthernbeaches.com.au/services/free-classifieds/?adpage=mainad&ad_id=4...uses the second technique with pretty photo, not fancy box.