Forget about using WinonCD. Get something like WinISO, you can use it to extract the boot record, drop and drag the files you want into the image, add the boot record and save as blahblahblah.iso. There are some other ISO programs that will do this too, but this one seems to be the easiest so far. I was going in the same direction as you until I discovered WinISO, because all of the help forums said to use Winon or some other burning software, but those just take much longer to put everything together. If you decide to go with WinISO, just make sure to name the image exactly as it is on the original.