I used "iso2usb" to create a RHEL 6.3.boot stick directly from CD.
When I boot the system with this stick, grub shows with the correct menu. It loads the kernel and shows the blue install screen.
Then a message appears about not being able to find the cd/dvd allowing me to press "Ok" or "Cancel".
If I choose "Cancel" I end up in a menu allowing me to specify which installation media to use (nfs, cdrom, local disk, etc.).
I choose "local disk" and get asked wether I would like to use "/dev/sda1" (USB thumb drive), "/dev/sdb1" (local HDD) or "/dev/sdb2" (local HDD). I choose "/dev/sda1" and the anaconda installer is loaded.
However the anaconda installer is moaning about not being able to find an installation source and then it stops.