Apparent duplicates are at http://bugs.python.org/issue1298962 and
http://bugs.python.org/issue1565468. This bug seems to have something to
do with "power user" user privileges.

I can duplicate this problem with the MSI installers for Python 2.4.4,
2.5.2, 2.6b1, and 3.0b1. According to some of the other issues, this
problem has been around since 2005; I really, really would like to see
it fixed by the final releases of 2.6 and 3.0, because, as Ross said,
this bug can be a showstopper for many enterprise users who encounter
it. (Or, at least, it forces us to find an administrator to install
Python even though we theoretically have install privileges for it.)

I've attached two logs from a Python 2.6b1 install on Windows XP, one
for a "just me" installation and one for an "all users" installation. In
both cases, I selected all options except for registering extensions.
Since I did this on my work computer, I have search-and-replaced the
values of LogonUser, UserSID, USERNAME, and COMPANYNAME to make them
generic.

Adding at least TARGETDIR to the SecureCustomProperties with Orca allows
me to install where I want to. It may take some investigation to
determine which properties should be added to this list and which don't
need to be.

I'd be happy to provide any more information that can help get this
resolved.