Install RHEL 6.4 from usb drive? Possible?

Downloaded complete install DVD ISO fir 6.4 and burned to USB (as per instructions for 7.1). No DVD drive on this server.

Boots ok, asks me for location (no option for USB so I select hard drive), so I select /dev/sda. Goes though location, hostname etc but then fails with error

"The installer has tried to mount image #1 but cannot find it on the hard drive. Please copy this image to the drive and click retry".

Is it even possible to install 6.4 this way from USB?

Or is it best if I get portable DVD drive put image on there, boot from usb (as I've done) but select DVD drive as install?