In the simplest case, the Amazon – Denver lookup Greasemonkey script will, when looking at a book on Amazon, will perform a lookup of that book within the Denver library and put a link on the page, just under the item title and author, to go to the item. See the image for what this looks like:
To install, first you need to install Greasemonkey.
After that, then click the “Install” button on the Amazon – Denver Lookup Script page. After installation, the Greasemonkey manage user scripts dialog (Tools->Greasemonkey->Manager User Scripts) should look something like this: