[Zope] dtml-methods in CMF/Plone ?

hi, we´re developing an application with lots of dtml-methods which call sql-methods and want to use cmf resp. plone as the content management framework ;-) all i can add inside a plone folder are generic plone/cmf objects: documents and stuff - adding a dtml-method with <dtml-var standard_html_header> and <dtml-var standard_html_footer> works, but calling it fails with "portal_url not found" tried that some weeks ago with an older cmf version, which worked out o.k. is there a way to use dtml-methods in a cmf resp. plone site / does it require special variables being passed? thank you a lot for any hints, oliver