As said above:
1) it has to be an ISO for an iso extractor to work.
2) it may be a compressed iso in which case you get to figure out which compression type and download the software to unpack it. I just try the various ones until something ID's it. winace, winrar, winzip, lharc, etc.
3) Some idiot may have hung an incorrect extension on the file which is confusing the unpack/iso tools.
4) Turn on the adult settings in wexplore (like show file extensions) so you can see what the file is claiming to be. Then click on the disk to show the subfiles.
5) Once unpacked then any iso opener should work. I prefer ISOBUSTER. Which will let you mount and run the iso without unpacking it or burning it to a CD.