[Zope] upgading to python2.1.1 on windows

I am currently using Zope2.3.2 on windows with python1.5.2. I need to use some functionality of python 2.1.1 which is also installed on the same machine. What is the easiest way to use the newer python with Zope? Changing the start script to use python2.exe instead of python.exe does not work. TIA