Thunderbird should import directly from Outlook but it may have
to be active for it to work. I can't remember how but I know I have done
it on an older version.
The is a support area for Thunderbird, so do a Google search for
"Thunderbird
knowledge base" you will get some response.

I did this once, a couple of years ago. If memory serves: I installed
Thunderbird *for* *Windows* on my XP machine, and imported the .PST file into
Thunderbird under Windows. Then I transferred the Thunderbird profile to my
Ubuntu machine, and attached it to the Thunderbird installation under Ubuntu.

There's a proprietary Windows API that Thunderbird needs to import .PST files.

It doesn't pick up contacts, calendar information or tasks from Outlook.

Both Thunderbird and Evolution import diresct from a 2003 .pst file - I don't
think they will from a 2007 .pst.