Sarah, if it helps, this is how to determine the version of the backup file, which is basically a tarball (TAR/GZ archive)
- Open the XXXXXX.MBZ backup file in 7-Zip, WinRAR or similar
- Extract the single file within
- rename the single file within to XXXXX.TAR
- Open the TAR file with 7-Zip, WinRAR or similar
- Read the file 'Moodle-backup.xml'
You'll be presented with a bunch of useful info on the backup, including version info.
regards, Andrew