I have installed from the full install DVD on a USB stick numerous times.
easiest way I found to do was to copy the ISO image to the USB using dd (this will delete anything on the flash drive)
dd if=Fedora-14-x86_64-DVD.iso of=/dev/sdp
(My usb flash was device /dev/sdp, replace with whatever yours enumerates to)
The set your bios to boot from USB, and reboot.