I messed up the bootloader by accident on a standard Centos 6.3 install because I turned the /dev/vda1 boot partition into an mdadm raid 1. This was all done correctly aside from one point Ididn't realize was an issue metadata=00.90 is the only thing that will allow you to boot (otherwise grub won't work and you won't boot).
So the next step is rescue mode from a CD right? The problem you will find is that grub does not detect your hard drives, this is Ibelieve is be........