Hi,
we don't currently have any documentation on the internal structure of the nfo files but we do have some information on file naming http://www.mezzmo.com/wiki/doku.php?id=supported_external_metadata_files&s[]=nfo. We also have a patch which allows exporting metadata from Mezzmo to nfo files to make it easier to create them so if you would like to try the patch please send an email to support [at] conceiva [dot] com.