The best way to back up all folders and messages complete is to copy ALL the .dbx folders from the Store location which can be found by looking and copying the path from the Tools/Options/Maintenance/Store Folder tab .. this will typically be the path .. C:\Documents and Settings\'User Name'\Local Settings\Application Data\Identities\{.. ..}\Microsoft\Outlook Express
These folders replace ALL the new installation .dbx folders
You would need to unhide protected /system files and show extensions in Explorer/Folder Options to see this path in an Explorer window.
To use the Import Wizard .. it would need to see a complete set of folders in a backup store or on a different drive somewhere.
Check the old and new store folder for the set if they are in different places.