Im about to give this a whirl. Should be interesting. Half an hour of research has revealed that its not exactly easy to accomplish this but we’ll give it a whirl anyway! 
Update: OS 9 is pure and total horseshite, as is Outlook 5 for it!
Update: SOLUTION!!!
How to extract email messages from OUtlook Express 5 on Mac OS9
Requirements: Paitence (lots), Entourage 2001, ImapSize (http://www.broobles.com/imapsize/download.php)
Open Entourage 2001 on the Mac, and import your OE profile. Once this is done you can drag the Message folders to the desktop. This will automatically save them into MBOX format. Once this is done. Move the MBOX files to the new machine, and use IMAPSize to convert them to eml messages. Then open Live Mail and import the emails.
How did you go with the transfer ? I heard mainly horror stories about getting Outlook Express data off a PC and onto a Mac.
Many sites say convert to Eudora OR Thunderbird and then Transfer to the Mac. Even these still are not 100%. As I have a substantial amount of emails, attachments, addresses etc I must get this right.
I have OE 6 and the latest Imac OS X (V10.5.4) Any further info appreciated.
Cheers
C
Hi Craig
It was long and it was painful to be honest. The only reason i didnt install any alternatives is because i couldnt, the OS was too old. If you have the latest OSX, you should be able to install an alternative and then import from OE6 (Eudora should be able to handle this)
An alternative is to drag the emails to the desktop, as in select all emails, click and drag them onto the desktop or a folder. This should pull them out as EML files, which you should be able to import
The address book, thats not so much of a problem. Have a look here: http://www.tuaw.com/2006/01/05/finally-a-tool-for-exporting-address-book-to-thunderbird-and/
If i recall, i just exported to a CSV, then mapped the correct fields when importing. It took some trial and error.
Let me know if you have any other questions. Unfortunately i dont have access to the original machine in question, but i’ll do what i can