From Cathal Connolly on the DotNetNuke forums:
"
you do not need to change the url for sitemap. The physical file sitemap.aspx exists in the root folder, and automatically creates a sitemap based on the data in the database - the UI in this case is badly chosen, it should not be showing a non-editable textbox it should be a label. You can see your sitemap file by typing
http://www.yourProductionURL.com/sitemap.aspx"