I don't think that Vista Mail recognises .pst from Outlook, unless you have Outlook 2007 on the machine.
I recently had to transfer my old emails from outlook to a vista mail machine and I used the info from the following web site and it worked fine......
http://www.directron.com/movmail.html
However, it will only work for Outlook Express to Windows Mail, so firstly set up Outlook Express 6 and import your messages from your outlook .pst then follow the instructions for OE6 mail folders to copy your messages from their storage folder. They should end .dbx
Use the import messages setting on vista mail. I think its File>Import>Messages, then messages from OE6 and select the folder from above. It will import the messages into Vista mail in a folder called Imported folders. You can then move the messages into whatever folder you want.
As far as entering email accounts I just wrote the settings down and manually entered them.
I believe another way is to download and install the trial version of Office and then import your settings and .pst and then transfer the messages to vista mail and uninstall the trial version!!
Hope this helps, good luck!
Edit. PS When I refer to OE6, I mean on the old computer and then copy the folder/files to a cd/sd card/flash etc