I've been asked to write a master page where one of the navigation elements will be a list of the sub sites to a site. Elsewhere on the page I've got another element which should be navigation for within the site as you would normally have, except without the sub-sites.
Can this be done with the PortalSiteMapProvider, or am I into the realms of writing my own

Using PortalSiteMapProvider to show only sub-sites
Suresh .M.V
Evan Hennis
This blog entry explains how to customize the tree view to show only sub-sites. If you want 2 tree views simply copy the code to another location and change id's to so that your tree has a unique id and refers to a unique sitemapprovider.
http://spstips.blogspot.com/2006/07/modifying-wss3-tree-navigation-control.html