Meifo's instructions should work fine for getting the Windows Mail messages transferred to Outlook and then porting the Outlook PST file to the new Windows 7 install.
However, I don't believe Outlook 2003/2007 have an EXPORT function for the actual email Accounts
. In prior versions email accounts could be exported to IAF files. I suggest you write down your friends email account(s), settings and passwords before doing the migration.
Also, if your friend is interested in using Windows Live Mail for its mobility aspects, the Outlook Connector enables the Outlook to be used as a Windows Live Mail interface.