Hi Mat,
If you have used the defaults, then you need to backup the following directories:
C:\Documents and Settings\_USER_\Local Settings\Application Data\MyPhotoIndex\Data - Holds the default index file(MyPhotoIndex.mdb - this is the most important file)
C:\Documents and Settings\_USER_\Local Settings\Application Data\MyPhotoIndex\Cache - Holds cached thumbnail files(*.icf extensions).
if you want you can backup the settings file (holds some size and preferences) :
C:\Documents and Settings\_USER_\Local Settings\Application Data\MyPhotoIndex\userSettings.config
These are the primary files.
Regards,
Asaf