I don't think opening the files is as much a problem as finding software that is compatible with mac. I don't really know of any standalone chess programs that are compatible with mac since I'm a windows user.
Have him try viewing them on a chess website analysis board. He should be able to upload the PGN.
One of my students was having difficulties opening PGN files on his Mac. Has anyone else encountered this problem? If so, how did you work around it?