PS3 can natively play MP3/WMA, JPG/PNG/GIF/TIFF for the Audio and Pictures, for the video, per the PS3 online manual at
http://manuals.playstation.net/document/en/ps3/current/video/filetypes.html you can play the following:
The DLink NAS does not do any transcoding of videos not in the above types, and not all AVI and MP4 files are necessarily encoded as above. You will need to convert your ISO or VOB file to one of the above in order to play via your PS3 (see programs like WinFF, VLC, FFMpeg, Super for this ability, plenty of guides if you look up how to convert videos to PS3 format).
Good luck!