re: outlook .pst files. http://kb.mozillazine.org/Import_.pst_files

This doesn't solve my problem. My Outlook and Thunderbird files are on the same computer.

well I have read the question and the answer and the response and seriously I have no idea what your talking about TwoLeftFeet.

these instructions are fairly clear

3. Copy the outlook.pst file to that PC and configure Outlook to use it. (may need to be in the default location) 4. Compact the .pst file using Outlooks File -> Data File Management commands to permanently get rid of any deleted messages. Don't confuse this with compressing or zipping a file. 5. Import the messages using Tools -> Import -> Mail. You can use Tools -> Import to also import the settings and address books. Repeat steps 3-5 as necessary for any other .pst files.

You obviously do not need steps 1 and 2... as you say your files are on the same computer.

And you files are on the same computer so steps 6 - 9 would not apply.

At the link I provided, there is another link to this: http://freecode.com/projects/pstimportplugin/?branch_id=72191&release_id=265973

did you try it?