The Personal Folders File (.pst) is a data file created in Microsoft Outlook to store all your email messages, contacts and other Outlook information on your computer. If you're using Outlook 2003 or 2007, the default PST file format is slightly different than the format used in Outlook 97-2002. This new format is called the Microsoft Office Outlook Personal Folders File. It has greater storage capacity and supports multilingual data, known as Unicode data. You have no direct way to convert your Outlook 97-2002 PST file to a Unicode PST file. The best way to do so is create a new data file in Outlook 2003 or 2007 and import the old data into it.
Open Microsoft Outlook.
Click the "File" menu. Select "Data File Management." In the dialog box, select the "Data Files" tab. Click "Add."
Click "Office Outlook Personal Folders File (.pst)." Click "OK."
Type a file name for the new PST file. Click "OK." Type a display name for the folder in the "Name" box, which is what will appear in the Navigation Pane. If you want to secure the file, type a password and verify it. Click "OK."
Click the "File" menu. Select "Import and Export."
Select "Import From Another Program or File." Click "Next."
Select "Personal Folders File (.pst)." Click "Next."
Enter the file name of the old PST file in the "File to Import."
Click "Options." Specify how you want to import duplicates. Click "Next."
Select the folder from which you want to import the file. Click the top folder and select "Include Subfolders" to import the whole file.
Click "Import Items into the Same Folder in." Select the newly-created PST file.
Click "Finish." Your old PST data will be imported into the new file.