The initrd.img in the images/pxeboot directory looks much smaller than it was in Fedora 16 and complains about an empty or non existent root= option when booting (http://dl.fedoraproject.org/pub/alt/stage/17-Alpha.RC2/Fedora/x86_64/os/images/pxeboot/ vs. http://dl.fedoraproject.org/pub/fedora/linux/releases/16/Fedora/x86_64/os/images/pxeboot/)