The first thing you want to do is let Outlook 2007 create its own PST file
because of the new format it's in. Then add the old Outlook 2002 PST file to
the Windows 7 PC and add the PST to your Outlook profile. Then simply drag
and drop the emails from your old PST into the new one.
You don't want to use the old PST because it has a 2 GB size limit on it for
one thing. Outlook 2007 doesn't have such a small limit set on it.