Do you mean a sitemap for the search engines (XML file for Google Sitemaps, etc.) or a sitemap that gives the user an overview of all your pages?
I'm assuming you mean the latter and if so, the page below talks about sitemaps but I'm not sure it's what you're looking for. It creates a graphical representation of your files but I'm assuming you want something you can publish for your visitors right?
http://www.adobepress.com/articles/a...83787&seqNum=8
I just created mine manually. I've never seen a function in Dreamweaver to create what I would want.