If you want to wait until after you've compiled your sitemap to publish your website, you'll need to install a Web server on your computer. Don't worry, this is actually pretty easy. Just do a Google search for free web server software for windows and pick whichever option works best for you.
Once you have installed a server on your computer, launch Sitemapper and enter the location to your website files in the Website URL field. (The format might look something like this: http://localhost/ or http://YOUR.IP.ADDRESS/. For the exact location, you should refer to the documentation for the server you installed.) Now you can scan your website and create your sitemap normally.
Once the scan is complete, edit the saved HTML and XML and do a search and replace for the local domain to the correct one.