Thunderbird Message Folder to Outlook?
 

I've been casually using Thunderbird and find it to be much faster and easier to use than Outlook/Outlook Express.

But I'm stumped when it comes to exporting/converting the mail files to .pst format.

Is there an easy way to do this?

I think you're asking about going from Thunderbird to Outlook. If yes, see "Importing and exporting your mail", then scroll down to "Export mail into Outlook (Express) or Apple Mail": http://kb.mozillazine.org/Importing_...ting_your_mail

Searching the Mozilla support forums yields the same answer, 1, 2, it's not a straightforward, one-click process.