If you do not also have Outlook ( preferably an up to date version)
installed, you will not be able to do anything with a PST file. Without
Outlook also being installed on the same computer, a PST file is just a
collection of unreadable junk.
The drill is to open Outlook, then open the PST file in question in Outlook,
and then you can import/export from that open instance of Outlook into
Windows Mail. Or on the old machine, export from Outlook to Outlook
Express, then on the Vista machine, import from the Outlook Express message
store folder (which will contain all the old DBX files used by Outlook
Express).