How can I export an MS Outlook .pst file to Apple Mail?
Do it via an IMAP server, which you can install on the Mac. I used dovecot, created an account on it, added that account to Outlook and just moved it all over. Then in Mail, I created the same account, and copied everything over.

I prefer this method because it completely preserves all the properties of each message, including attachments. Exporting and importing through another method (including Thunderbird) doesn't preserve everything properly.