How do I backup Outlook 2007 files?
Can I use these backed up files with Outlook express? Where is the default location for these files?
File > Data File Management
Put your mail in .PST's. Copy them to your backup location. Outlook may need to be closed to copy them.
I'd recommend using Microsoft's free Personal Folders Backup tool. It runs when Outlook exits, and has simple schedule support ("every N days").
I'd then copy the backup to a USB stick, an online storage account, or some other off-machine storage for safety.
As far as Outlook Express (Windows Mail in Vista) is concerned it does have an import wizard, via File menu, Import, Messages.