When you burn the boot.iso image, make sure that you select the option to burn an image file to disc in your CD burning software. The exact wording of this option varies, depending on the software that you use, but should contain the word "image". Note that not all CD burning software includes this option. In particular, the CD burning software built into Microsoft Windows XP and Windows Vista does not offer this capability. There are many programs available that add this capability to Windows operating systems; Infrarecorder is a free and open-source example available from https://www.infrarecorder.org/.