That's the whole point, Windows Mail DOES NOT RECOGNIZE a .PST file at all,
not even a little bit.  WM, like Outlook Express before it, use Outlook
(which DOES recognize .PST files) to access the .PST file.  You, therefore,
MUST have Outlook installed in order to get anything from or add anything to
a .PST.  This leaves you two options:

1. Install Outlook on the Vista machine, copy your existing .PST file to the
Vista machine (DO NOT OVERWRITE any existing .PST files in this process),
open the .PST with Outlook (File|Open|Outlook Data File), then do your
import into WM.

2. Transfer your data from Outlook to Outlook Express on your old machine
(which has both programs installed), copy the OE .DBX files (including
Folders.DBX) to your Vista machine and import these into WM (which works
because WM DOES recognize Outlook Express files).

Hal

If you still have the CD that installed Outlook on your old computer,
use that to install it on your Vista machine. It may not activate if you
have used more than the allotted number of installs, but it should be
sufficiently active to help with the import.

If you don't have your old CD for it, some, but not all, of the free trial
versions of Microsoft Office include Outlook.  That version should run
more than long enough to use it in the import.

http://us1.trymicrosoftoffice.com/default.aspx?re_ms=oo&culture=en-US