(1) you will need access to vista Windows mail. In his case your wife still has.
(2) Read this plus comments: http://www.mydigitallife.info/download-windows-mail-from-vista-for-use-in-windows-7/
Ok, the link to get the files/programs is no longer valid. So:
First you need to copy the Vista windows mail folder to a thumb drive, But first you must change the permission so that you have full control. Added - Don't forget to Export your old win mail emails and address book to a file and also put on thumb drive. Note: You can replace "thumbdrive" with external HD or DVD disk.
After you have installled window 7 to rename the Windows mail folder to say Old Windows Mail.
Then copy the folder from the thumb drive into windows 7 (Put it in the same folder that had the orginal windows 7 Windows mail folder (Should have been prorgam files).
Click the winmail exe file.
I'm looking for a better explanation. http://social.technet.microsoft.com/Forums/en/w7itprogeneral/thread/f148569e-a699-41f9-8679-3a1c12c110e9
This one seems pretty good: http://www.techspot.com/vb/topic137494.html