And as for simultaneous 64/32-bit Python installations on a single 64-bit machine - as Paul said, whichever way Microsoft implemented its automatic registry key redirection, it is up to Python to decide how its installer should behave.

So the question is - should it be possible to run 32-bit & 64-bit Python installations on the same machine using the standard py.exe wrapper when those installations are done for the current user only?

I know I found that useful in a scenario (done using installations 'for all users' though) where I had some scripts using 64-bit Python and needed to run several scripts automating a 32-bit Python extension module. I believe the problem was in the pstools module that at the time was not available as a 64-bit build (don't know if that situation has been resolved since).

Personally, I just noticed the undocumented inconsistency and decided to report it. I don't really care all that much about whether it is resolved cleanly, as in my development setup I have other problems preventing me from using the py.exe wrapper all together - I need multiple parallel patch releases in the same system and the best way I found to achieve that is to:
  - do a 'local user installation' - version A,
  - rename the target folder for version A
  - do a 'local user installation' - version B,
  - ...
and have my own version specific startup scripts like py243.cmd, py244.cmd, py276_x86.cmd, py276.cmd, py340.cmd, ...

I really don't like it that different Python X.Y patch releases overwrite each other's installation registrations or uninstall each other automatically. :-( Or that you can not specify more detailed Python interpreter version information like 2.4.3 to the py.exe wrapper. :-(