[Zope] Accessing folders

I'm new to all this, so please be patient. What I am doing at the moment is using <dtml-tree> to construct an html form of catagories for users to submit images to. I was setting the value of the radio buttons to tree-item-url and then hoping that I could just replace all '/' to '.' to access the folder that I wanted to image submitted to, and call manage_addImage. I was using <dtml-let> to assign a var to the folder url with the .'s and then calling <dtml-call "_[submitfolder].manage_addImage(id='', file=file, title='')"> Not working. Could anyone please point me in the right direction? Thanks. -Chris