There are specific programs such as ISOMaster which is available from
Getdeb.net. You can also do this from either Brasero or K3b (burners that come
with Gnome or KDE but will run in either desktop). The trick is not to burn it
to your DVD drive, but as an image file. It is done at the last stage of the
process. Add your files then select burn and change the device to an ISO image
file.