I'm trying to install Ubuntu 12.04 using usb pendrive.
I have made USB bootable. Setup starts but it's not showing "install from USB" option. It shows only "Install Ubuntu".
"Install Ubuntu" option there means, Install from USB, since you booted from USB.
There is no custom messages for CD and USB. All contain "Install Ubuntu" option. The other option is "Try Ubuntu" which Starts Ubuntu without installing giving you a chance to experiment with Ubuntu
Hope this will help.