MetFileRegenerator comes with PartMetBackup which is dependent on knowing your client's temp directory, so the installer will attempt to autodetect the install directory of your ed2k client. You are given the option to have PartMetBackup added to your start menu so that it can be run in the background to backup your .part.met files every hour. You can also choose to associate MetFileRegenerator with your .part.met files so that when you double click on them you are brought to the View/Edit mode.

How to recover lost downloads
Run MetFileRegenerator in recovery mode and select the download to recover.
If PartMetBackup has a copy of your file's .part.met file the option 'Use backups from PartMetBackup' will be available and selected. This will quickly copy the file over and allow you to continue the download in eDonkey/eMule, but it may not necessarily recover everything you've downloaded. If you want to try and recover more deselect the box and click next.
MetFileRegenerator will now hash your file and try to find a match. This process takes some time, but it will not need to be repeated until your file is modified again.
A list of matching files will be presented if any are found. If the proper file is listed, select it and press next. If the proper file is not listed or no candidates are found then you will need to restart the download to help MetFileRegenerator get the appropriate data.
Use eDonkey/eMule's search function to find the exact same file (or use an ed2k link if you remember where you got it from).
Use MetFileRegenerator's View/Edit mode to check the .part.met file of the download you've started. Once the crumb or chunk hashes are present you can try recovering your original download again.
If a candidate is found click next and then cancel the download you started in eDonkey/eMule and restart eDonkey.
If no candidates are found and the crumb hashes weren't present, wait until they are and try again. If the download still cannot be recovered then you did not download the right file or your download doesn't have enough valid data to recover.