Can I install F18 from harddisk or usb just as F17 or before?

I had tried to install F18 beta TC5 from harddisk or usb as installing F17 from harddisk or usb. But they all failed, they told me "can't find /root" or something like it. I don't remember it exactly.
I want to know if I install F18 only from DVD at present? If I can install it from harddisk or usb, how to do it?