I found a solution on this very forum - it worked almost perfectly for me, although I didn't get the attachments. I'll just paste it here:
The fix by ScottiouS above got me all the way from Outlook on WinXP to Mail in Mac OS 10.5 via Thunderbird. Here's a walk-through of the steps for clarity. Thanks everyone for posting the helpful info...
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How-To - How to transfer PST files from Outlook (Win XP) to Mac OS X 10.5 Mail (2008.08):
Install Mozilla Thunderbird on the PC
When opening Thunderbird for first time, let it import all emails and contacts (select "Outlook" from the drop-down menu)
This converts all your files to the mbox format (note that no suffix appears after the file name for mbox files)
Locate the Thunderbird mail files. In Win XP, the location is something like this: C:\Documents and Settings\[username]\Application Data\Thunderbird\Profiles\[eightcharactercode].default\Mail\Local Folders
Copy the folders/files you want from the PC to the Mac using a USB drive, etc.
Download the free Eudora Mailbox Cleaner program onto the Mac:
http://homepage.mac.com/aamann/Eudor....html#Download
Open the Eudora Mailbox Cleaner and put the .app file into the Application folder (or the desktop)
Make sure Mail is closed on the Mac
Simply drag the copied master mailbox folder (or specific folders) onto the Eudora Mailbox Cleaner.app icon, then select "Thunderbird" as the source
After opening Mail, look for the "Imported" mailbox folders
You will need to select each new mailbox individually, then click Mailbox -> Rebuild from the menus to populate email mailbox
That's all!