What he said. OE does not exist past WinXP, so he has to switch mail clients anyway.
I would install Thunderbird on the XP machine, import his OE mail, etc., then copy the contents of "C:\Documents and Settings\user\Application Data\Thunderbird" on the old machine to "C:\Users\user\AppData\Roaming\Thunderbird" on the new machine.
If he'd rather not use Thunderbird, then first install Live Mail on the Win7 machine and use the official MS transfer wizard to handle the heavy lifting, or install Live Mail on the XP box, have it do the import, then do the xfer wizard to the new box that has Live Mail on it.
You have to install Windows Live Mail on the Win7 box because there /is/ no built-in mail client.
Think for yourself, schmuck!
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