Windows Mail cannot import a .pst file unless Outlook is installed on the
Vista computer.
You can install Outlook, copy the .pst to the Vista computer, open the .pst
with Outlook, then you can import into Windows Mail.
Or,
If you have Outlook installed on an XP computer, import the .pst data into
Outlook Express, copy the .dbx files and .wab file to the Vista computer,
and import into Windows Mail.