Do you use Windows Mail on your Windows 7 ?
And if so, did you manage to get the files overwritten by the Windows Mail Files, placed in the \Program Files\Windows Mail Folder on Vista ?
Otherwise the Program won't run, but done correct, Windows Mail does the job, there are two problems, if one sees it like that, you can't click on the "Read Mail" button on the IE Bar upper right, and it's not working with the .eml to open them with Windows Mail.
Still dragging them into Folders in Windows Mail, makes the readable again.
PS! If your Windows 7 RC is some bit off the road, try with a newer, like the 7600 ZUKO, seems like the Build you'll get in the end, anyways!