If the iso file is named foo.iso and you have an empty dir named isoview:
mount foo.iso isoview -o loop
then cd into isoview and look around and cp to your heart's content.
You need loop device support in your kernel and loop devices in /dev (which you most likely have).
Pretty sure that altering anything in the mount dir (isoview in this example) will trash the iso file. You may not be able to alter it, it may be read only. But cp'ing a file out is no problem. The mount command may require you to be root. Oh, and loop support is not the same thing as the loopback (127.0.0.1) interface, that causes some confusion.