Logged In: YES 
user_id=206950

Ok, maybe the summary is misleading. The
HKEY_LOCAL_MACHINE\Software\Python subtree appears to exist,
with PythonCore and Pythonwin subtrees under it. Under
PythonCore is a 2.3 subtree and a 2.4 subtree. This implies
the installations work side-by-side. I found nothing
explaining whether to uninstall a previous version or not in
the docs on Python.org, or whether it is possible to upgrade
a previous version by installing into the old directory,
etc. In particular http://www.python.org/2.4/msi.html avoids
this issue. I had guessed that maybe the move to some sort
of official packaging system was because it would enable
these automatic updates, somewhat akin to RPM, but obviously
not.

I can't comment on how the installers for add-on libraries
on Win32 are made (although it seems to use a standard
package), only that I get no option to install them into the
2.4 directory, at least given the 3 I've just tried.