How to make an image of a bootable dvd

Daemon Tools and Imgburn have an option to create iso. Or if you have Nero installed, you can copy the disc to NRG image and then convert it to ISO using the light application Any To Iso. This method is easier if you have Nero installed already.

This explains what makes a CD/DVD bootable

The image will carry the ability to be boot-able.
All you need is to get the image out with some tool.
You could then burn the image to a blank DVD.
ImgBurn will let you do these things.

This gets complicated if the source DVD is DRM protected.