Some machines, like mine, are finicky. I've tried disk drill, disk creator and Apple's method. It was tricky, some machines accepted the install usb as disk drill, etc. made. Every one accepted the original snow leopard installed. I was going to choose one of those USBs as startup drive, then I couldn't see it listed as something to boot to. That's when I understood and checked the theory. I found the DMG file I needed to install and then used Disk Utility to restore to a USB.