I'm a newcomer to CentOS. Fedora 14 was the last Fedora version I managed to make work. Fedora 16 I couldn't install at all. Fedora 17 installed, but I couldn't make it work right. I'd been trying to do media-less installs because Fedora wouldn't read my DVDs anymore.
What directions I could find for installing CentOS without media were not all that clear to me, so I did some guesswork informed by some of the Fedora documents.
I used the following grub stanza: title Install Centos 6.2 from net install iso find /centos/vmlinuz root (hd1,9) pause paused kernel /centos/vmlinuz method=http://mirror.anl.gov/pub/centos/6/2/os/i386 initrd /centos/initrd.img
The find and pause were not really necessary. I think vmlinuz and initrd.img were copied from a net_install.iso file. Much to my surprise, it worked the first time.