installing windows from bootcamp with image dvd
You cannot use an ISO image with the Boot Camp Assistant. It only allows a disc, as:


You need to install it outside of Mac OS X
You cannot mount an image when Mac OS X is not running
Mac OS X's EFI bootloader only accepts physical storage media


Thus, you can only use a disc. To burn the ISO to a CD/DVD, mount the image, open disk utility, insert a blank disk and click on burn. After burning the disc, you should be able to use it for Boot Camp.