This previous hint suggested moving contact info from Outlook to Mac using libpst. But libpst is also useful for moving zillions of mail messages that are stuck on a switcher's (in this case, virus-ridden) Windows laptop. Of course, there are shareware apps (like the excellent O2M), but if you like to get your feet wet in the Terminal (and presuming you have Xcode installed), try this:
Then open Mail.app, choose Import Mailboxes... from the File menu, and pick Other as the type. Then look for the output folder where you saved the converted email, and sit back while Mail.app imports all the messages.
readpst -o /path/to/output/folder /path/to/somefile.pst
Mac OS X Hints