You don't need to hex edit anything, that's overkill.
Some seem to have had luck using Daemontools to "mount the image." But you shouldn't have to do that to get it to work.
Try starting over. Completely uninstall the game (but first copy all the saved games and control files to a separate folder for backup). Then use a free (trial) program like "YourUninstaller2008" to completely remove everything. Start fresh from the original, official discs in a new directory, apply the official patch (1.01) and go from there...
You might also try JKhub.net which has some unofficial patches that might help if it's your video card, etc.
JK_.cd should be copied from the official CD1 for the first half of the game and (if needed) cd2 for the second half. I wouldn't recommend using a crack for Single player though, frankly. For MP, either one will work (I usually just copy it from disc 1 for that purpose).