Mike Gannotti has instructions posted on his blog for adding the PDF icon to SharePoint 2007 as well as the steps required to install the PDF iFilter and include the File Type in the content index. He even links to the correct places on the Adobe site where you can not only download the iFilter but also the correct 17 x 17 icon. Nice work!
This is one of many posts that I add to my blog to save me to trouble of looking for the link later since I am sure I will refer to it again. J