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