The "Windows Mail" email client (WM) is only available on Windows Vista.
You may download the new Microsoft offering named "Windows Live Mail" (WLM) for use on Windows 7 (see: http://download.live.com/wlmail ).
WLM looks similar to WM but it is a completely separate program. You may transfer WM mail messages (from Vista) to WLM (on Windows 7) as follows:
1 - install Express Assist 10 (EA10) on the Vista machine
2 - make a backup copy of the WM mail folders on the Vista machine
3 - copy the backup file from step 2 to the Windows 7 machine (or to some media that can be read on the Windows 7 machine).
4 - install EA10 on the Windows 7 machine
5 - run EA10 -- click "Restore"
6 - locate the backup from step 3 and "open" it.
7 - choose restore option "Restore All Email Folders and/or Data Files"
8 - select the "Windows Mail" group (on the left)
9 - select all of the Mail folder items and the mail index data base
10 - click "Restore Now" -- the EA10 program will restore the WM mail messages
11 - start "Windows Live Mail" (WLM)
12 - go to menu "File" - "Import" - "Messages"
13 - select "Windows Mail", click "Next"
14 - the proper location will already be filled in, click "Next"
15 - select all of the mail folders you wish to import (hint: hold the control key or shift key while selecting multiple folders)
16 - finish the import
Notes:
The import process will place the WM mail folders under an "Imported Folder" in WLM . That is, the WM Inbox messages will not appear in the WLM Inbox, etc. This is not a bug in EA9. This is just how Windows Live Mail handles the import. You may re-arrange the mail folders after the import using "drag and drop".
The Windows Contacts can also be transferred to Windows Live Contacts as described in this related article.