And especially what planetscape wrote

The issues that you and she outlined can be avoided by paying due diligence to the content of your PATH.
On my Windows machines, there are no perls in my default path.
If I want a perl in my path, I have to add the one I want - by opening a Cygwin bash shell, or by executing a batch file (portable Strawberry's portableshell.bat, or one of my own customized .bat files).
That way, I'm generally set up to avoid those types of problems, without even having to think about them.

Cheers,
Rob