[Zope] How to render tales in strings in a script

Hi, I need to render a string (not a zpt-object) with tales like <img tal:attributes="src here/images/spacer.gif/absolute_url" src="spacer.gif" alt="" title="" border="0" width="1" height="15" />. Does anybody know how to do this in a script? I already know how to import PageTemplate.py and it should work with read() or pt_render() or document_src() but it does'nt. :( I get unauthorized errors. -- many thanks for your replies, Elena