[Zope] Passing paramaters for form processing

How do I set some parameters for use in a form processing method? I have a HTML "FORM" tag referencing a DTML method name, and I want that method to have visibilty of some variables from the calling methods space. I've tried passing them with the url (eg, "ACTION=/someurl?fred=<dtml-var blah>") and by using REQUEST.set syntax in the calling method. Neither seems to result in the variable being visible to the form processing method. Any ideas? Steve