Yup, I would recommend Thunderbird. I imported everything from Outlook Express at version 0.6 or so and it was fine. Looking at the "Import" function it appears to be able to import mail and settings from Outlook.

All your mail and settings will still be as they were so you can uninstall it if it doesn't meet your requirements. The multi-account functionality in Thunderbird is very good though, it should do everything you want.

Gareth