FreeBSD 5.x Mount

 # mdconfig -a -t vnode -f image.iso -u 0

mount -t cd9660 /dev/md0 /mnt/whatever

FreeBSD 5.x Unmount

 # umount /mnt/whatever

mdconfig -d -u 0

FreeBSD 4.x Mount

 # vnconfig -c vn0c image.iso

mount -t cd9660 /dev/vn0c /mnt/whatever

FreeBSD 4.x Unmount

 # umount /mnt/whatever

vnconfig -u vn0c