It is not possible to install more than one version of
Python 2.4 on a Windows machine with the current installer.

First time The installer is used, it is fine. Next time
I have tree options:

Change, Repair & Remove. I need a "Install another
instance"

I work in Zope, and recently I have been developing in
Zope 3. 

Zope 3 is installed under "site-packages". If I only
need one Version of Zope 3, it is no problem. But if I
need both 3.2 and the current trunk from subversion, I
cannot do it, as I can only install one version of Zope
3.x per python. And with only one Python, that means I
can only have one version of Zope 3.x.

As far as I can figure out, this must be a general
problem for different library version that must be
tested on the same Python version.

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You _can_ install a given Python version multiple times on
Windows now, but to do so you need to set up a new account
(which is easy) for each one, and do "just for me" (not "all
users") installs of Python (and giving each a different
installation directory).  It can be a pain switching between
accounts, but that's your only hope for short-term relief.

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This is by the design of the Microsoft Windows installer.
Each MSI file is identified by package code and product
code. If you want to install the same package twice (in the
same account), you have to change all UUIDs in the MSI
package. I believe MSI "transforms" could help here.

I'm closing this as "won't fix". If you still think this
feature is necessary, please resubmit as a feature request
(RFE).