Fedora 18 should use rpmfusion free/non-free repos
Installing Free and Nonfree Repositories
yum install http://download1.rpmfusion.org/free/fedora/rpmfusion-free-release-18.noarch.rpm
yum install http://download1.rpmfusion.org/nonfree/fedora/rpmfusion-nonfree-release-18.noarch.rpm
Mounting the ISO image:
mount -o loop centos6.4.iso /mnt