[Zope] multiple select question

I'm trying to pass values from a multiple select to a property. The property sheet won't let me create a multiple selection though. It fails by claiming that the variable which defines the select elements can't be found. I can create a standard select with that variable though. The variable which defines the elements is on a property sheet higher up in my ZClass heirarchy and it is set to the type lines. Is this the problem? How can I set up a multiple select, or at least pass elements from a multiple select into a predefined property. Ultimately I wan't to create a catalog listing like KMNetNews has, but with multiple categories, and possibly subcategories. Thanks, Jason Jones jason_j@countermedia.org