I have Microsoft Outlook 2007 installed and use IMAP

I have Microsoft Outlook 2007 installed and use IMAP for all my mail accounts. When I updated to Windows 7 I had to reinstall Outlook and thus download all the headers again. I ended up downloading everything again, but I would want to prevent this in the future. Is there a way to import my Microsoft Office Outlook Personal Folders (.pst) or Offline Folder (.ost) files into the new installation, so I don’t have to download all the headers again?