The data files are all distributed on the CD-ROM in FITS format. The file format of all files is described in the ISO Data Products Document (IDPD), also distributed on CD-ROM. An example CD-ROM directory structure is given in an appendix of the ISO Data Users Manual.
The README.TXT in the top level directory on the CD-ROM describes the directory structure of the CD-ROM and what documentation files are placed where. The file DATALIST.TXT describes which observations are placed in which directory.