On Windows XP I get "No python installation found in the registry" when installing certain Products
Some Products need to know which Python to use and on Windows, will check the registry to determine that. When using the Windows installer for Plone 2.5 or newer, Python is not automatically added to the Windows registry. You can add the installer's version of Python to the registry through Plone menu from the Windows Start menu:
Start menu / Plone / Development / Set InstallPath
Alternatively (and this might be needed for Plone 2.1 and older Windows installers), you can install the same version of Python via a Windows installer which will add itself to the registry.