Potential Multiple installations of Python on Windows

I ran into the following problem: I need to supply the installation package to the client. Part of the code is python, so I have to make sure that it is installed. I am using NSIS for the installation ans would like to install python into a predefined by me folder (let it be c:\Program Files\Project\Python26). For that I downloaded the python's msi and trying to execu开发者_JAVA百科te the following to install it

msiexec  /package "$INSTDIR\packages\python-2.6.5.msi" /quiet TARGETDIR=c:\Program Files\Project\Python26

This works the first time (when python is not already installed), but if the python is already installed, I have to choose between reinstalling/repairing/changing. Does anybody know how to make sure that I can install python in the my directory without affecting potentially installed python?

Per the docs, options such as /p (or maybe /o or /c, depending on your exact intent) should serve your purposes.