[Zope] Zope Permissions

hi everybody! i have a little problem with permission settings. i'm writing a product in python. the product installs dtml methods when installed in a folder. now i want zope to ask for the user name and the password when a certain page is rendered as an URL (zope doesn't have a user name yet). i found out that in order to get the zope login window, i have to uncheck the view permission of the page (i mean the checkbox for acquire permission settings). how can i uncheck the box using python in my product? or how can i delete the view permission for this page in my product? i hope someone's able to help me here. thanks in advance, katrin