what I have done on my windows 7 is that I have installed both versions on it , then have created short cuts of each idle on the desktop and just use whichever I want . I think vegaseat has posts on this matter too
If you use an IDE like Ninja, then you can switch beteeen different versions of Python by following the tabs:
then simply edit the Python Path field.
If it shows
replace the 32 with 27