Importing big mail hierarchy into Evolution - how?

[Chris G]

I am moving my wife over to xubuntu from windows XP, the move has been
precipitated by the disk drive on her XP system dying.  Fortunately I
was able to extract all the data before it expired completely - but
that's another story.

She was using Thunderbird and Firefox on XP so the initial transition
to Linux has been fairly painless.  I have got all of her Thunderbird
mail on the Linux system now.

However it would be better if I could move her to Evolution because
that synchronizes "out of the box" with her Palm Treo - I have the
synchronization working already.

The trouble is I need to get all of her mail across from Thunderbird
to Evolution.  It's easy enough copying individual mailboxes across
but she has an extensive, hierarchical, mail archive with hundreds of
messages in a complex hierarchy of fifty or sixty folders.  It would
take forever to copy this folder by folder.

So, can anyone suggest a way to export the folders from Thunderbird
and import them into Evolution preserving the structure?  I have found
the ImportExportTools add-on for Thunderbird but Evolution doesn't
seem to understand the format of what it exports.

-- 
Chris Green