upgrade from 2003 to 2007 Outlook question

about to upgrade to 2007 office. not worred about the upgrade but worried
about outlook. my pop 3 acct that is setup, i download all emails and do not
keep a copy on the pop server. to make sure i keep all my emails should i
installed 07 first then remove 03 or just save my .pst files and then load
them into 07?