There is one more way to transfer mails from mac to windows. This is little bit take short time from imap.
Sometimes imap can not synchronous.
1 - Open a folder on desktop then drag and drop mails from outlook to folder on your mac.
2 - Copy folder to your xp, open outlook express, drag and drop mails from folder to outlook express's folder.
3 - Export mails to pst using outlook express.
Success