The official microsoft windows ISOs are already bootable. To check yours, open ImgBurn, switch to Write mode ('Write image file to disc' option), load the ISO image and look in the File Sys field: if it says Bootable then the image is ready for burning.
If it isn't bootable then you can follow this guide to create a bootable disc / image. By the way, if you need to extract the files from your non-bootable ISO image you can use 7-Zip / WinRAR / similar compression programs to do it.