[Zope] <dtml-with "portal_url.getPortalObject()"> gives AttributeError

I'm trying to keep around some legacy code, in zope 2.5.1 (CMF 1.3) trying to surround a block with <dtml-with "portal_url.getPortalObject()"> so I reference root level folders. I get the error: Error Type: TALESError Error Value: exceptions.AttributeError on getPortalObject (it's a bit of dtml code in a ZPT page). I've tried a variety of different evaluations, and proxy roles on the dtml method, with basically the same problem. Any idea how to do a dtml-with so you're at the root of a portal (also I'm using VHM)? M