I can right click, then from the drop down list select 'Open with' then choose 'Notepad'. You then have a choice to select a box for it to do that always for that type of file.
But I have just retried this & it always opens in Notepad, left or right click - I must have ticked that box! I use W7, which I think is virtually Vista I think.
I know if one tries to open an .xml file that is part of the plane you are currently flying & try to save it will tell you you cannot, because it is using it.
HTH
Keith