Mac Mail to Outlook

This is the best way I've found so far.

Here's some instructions on how to make it work (note: you will also need Eudora + free edition installed on the PC):

Starting in Mac Mail do the following for each mailbox you wish to transfer (In, Sent, Deleted, etc.):

Select all messages and choose File -> Save As from the main menu. Choose "Raw Message Source" as the format and a name for the group of messages and click the "Save" button. Even though there are no obvious "export" commands from Mac Mail, this will effectively create a file in standard mbox format. However, Outlook Express will not directly import this file type so we'll have to play with it a bit.

Transfer the file you just created to the PC.

Open the directory C:\Documents and Settings\[Account Name]\Application Data\Qualcomm\Eudora (you will need to go to the View tab under the Tools -> Folder Options menu and select "Show Hidden Files and Folders" to be able to view this folder).
If appropriate, rename the file you created in step 1 to match one of the mailboxes in this folder (In, Out, Junk, Trash, etc). Assign this file a .mbx extension.

Copy the file from the previous step into the folder you opened in step 3. (Important! Only do this if you don't mind overwriting the email in your Eudora application).

Open Eudora and view the mailbox you just copied. This will firmly establish your .mbx file as a Eurdora mailbox. Don't worry if the text in your messages doesn't look quite right - this will soon be remedied.

Open Outlook Express. Select File -> Import -> Messages from the main menu. Choose "Eudora Pro or Light" and go through the rest of the wizard. This should properly import all your messages from the selected mailbox into Outlook Express.

Once it's in Outlook Express it's an easy import into Outlook.