Currently the Import Utility that comes with Communicator 4.5 and higher does not support Outlook Express 5.
 
However, Outlook Express 5 has a feature that lets you export the mail files to the same format that Outlook uses. To do this:
 

1. Go to the File menu, select Export, then choose either Address Book or Messages depending on which you will be importing into Communicator. 
2. Follow the on-screen instructions to finish the export.
3. When you are done exporting your information, use Communicator's Import Utility to import the information into Communicator:
• Open Communicator.
• Go to the Communicator menu and select Address Book.
• Go to the File menu and select Import.
• In the Netscape Messenger Import Utility window, click Outlook 97/98 once so it is highlighted.
• Click Next.
• Select the mailboxes you wish to import into Communicator.
• Click Next (or click Skip if you do not wish to import mailboxes).
• In the next window, specify which address books you wish to import.
• Click Finish to proceed or Cancel to cancel.