I have been trying to free myself from Windows for some time now. Here is one trick I used to free myself particularly from Outlook for mail archives.
I have about 5 GB of archives of Outlook mail in pst files. As we all know, Entourage is gleefully ignorant of pst files and thus this was an inhibitor for me to get to my archives.
What I did to get around this: use Thunderbird under Windows to import all my mail from Outlook. Caveats: (1) ensure you have sufficient disk space (2) even better, but your TBird profile on a mounted Leopard disk inside Windows (mount z: to, say, Documents, create a TBird directory, and right-click Local Folders in Thunderbird and point the Properties page at the z:\TBird directory). The export took about 6 hours.
Now that I had my Thunderbird import of all of my Outlook mail, I started Mail in Leopard and did an Import -> Thunderbird Mail and pointed Mail at the directory used above. Mail took about 4 hours to import everything into an Imported Folders directory under On My Mac. I renamed this Outlook Mail. Then I used mdimport -E / to re-index Spotlight and now I have a completely searchable archive of my Outlook mail.
The only issues so far have been that in some emails, there are some HTTP and XML tags that are not parsed oyt by Mail and so occasionally the messages are unreadable. I posted a question to the Mac Mail Discussion forum here but have had no reply yet.
Hopefully, that helps someone out there…