"copy the cd iso to the usb"?
First, burn the iso image, not copy it, to the USB device with the some thing like UNetbootin. This will only make the device bootable.
Now, leave your USB device, nothing further needs to be done to it, and then configure your machine to boot through the USB device. Your computer Bios wouldn't do that as you said, so you need Plop boot manager to allow your pc to boot with a bootable USB.
You can write Plop boot manager to the hard disk or you can write it to windows boot menu or a cd or a floppy, and the plop manager will let you boot from your bootable usb drive.
There are various methods so you need to study plop boot manager section. This is a very simple way to do it. I think you are confusing yourself with plop linux section.