I don't know of a NAS-specific version of Air Video - only that of Plex (see http://wiki.plexapp.com/index.php/FAQ:_Plex_Media_Server_and_NAS ). The NAS***** one ( http://wiki.nas*****.org/doku.php?id=documentation:howto:airvideoserver ) isn't really running on commercial NAS servers (AFAIK). I may be wrong though.
EDIT: it seems the 4-free (remove the - from the word!) is a non-allowed word; hence the asterisks above. It doesn't seem to have to do anything with the NAS4-Free (again, remove -!) so I post this addition knowing I'm not breaking the rule - after all, the NAS4-Free project is just unlucky to have a, by spammers, commonly used character sequence in its project name.
Plex might be better for streaming directly from a NAS. But if you have a 'dumb' NAS, you can use Air Video -- just have the server point to the NAS directory on the Mac. Boom.