[Zope] Tree?

I was playing with Tree, from the point of view of using it as a dynamic navigation bar on a site. I've set up an index_html page that has a one row table with the tree on the left hand cell and a local page information on the right. If I don't put a starting location on the tree (i.e. <dtml-tree>) everything works fine, except that my nav bar always starts at whatever level I am. If I put the site root as the tree focus, (i.e. <dtml-tree foo> I get errors that standard_html_header isn't found, which is obviously false. Any clues as to what might be happening?