Okay the quick and easy option would be to spend $6 and rebuy the game on GOG.com. They will legally sell a copy of the game to you but also package it and test it to work on Windows XP, 7, 8 http://www.gog.com/gamecard/wing_commander_3_heart_of_the_tiger.
Otherwise what you may have to do is insert the first CD and get it to install some game files. Generally if you do a DIR command on the ISO mount there should be a file INSTALL.COM, INSTALL.BAT, INSTALL.EXE or something similar. ISO images are CD-ROM images, the ROM stands for Read Only Memory meaning you cannot write data to it. So CD games from this period generally installed part of the game to a computer’s hard drive (DOSBox C:) and used that for save games and temporary files.
