See:

http://shadow2531.com/opera/wiki/How to Manually Import POP Accounts from Outlook Express - Mail Client ( M2 ) - Opera Wiki.mhtml

and

http://shadow2531.com/opera/wiki/How to Import POP Messages and Retain Folder Structure - Mail Client ( M2 ) - Opera Wiki.mhtml

and

http://shadow2531.com/opera/wiki/How to Import Contacts from Other Mail Clients - Mail Client ( M2 ) - Opera Wiki.mhtml

After they're downloaded, open them locally to view them)