This is really easy. Simply add an image tag using this format for the src attribute
src = “http://thumbs.webshotspro.com/url/http://????”
replace the ???? with the URL of the page you want the thumbnail for and Webshots does all the heavy lifting. Now that is easy. The only stipulation is to provide a link back to their site, also they have a firefox plugin that puts thumbnails beside the stories on Digg and a bookmarklet to make getting the thumbnail URLs even easier..