[Zope] Problem with Zope Book example

Hi, I'm working my way through the Zope Book (using Zope 2.4.1 on Win2000), and have run into a problem in the "Using External Methods" section (p. 155). It describes an Extensions directory in the top-level Zope directory, which wasn't there in my installation. So I added it, added the Example.py file as directed, and followed the instructions to create an External method (id=hello, Module Name=Example, Function Name=hello). This gave me the message: The specified module, Example, couldn't be found. I tried it again with a blank __init__.py file in the directory. I also tried restarting Zope. Nothing. What am I doing wrong? Thanks, Michael