Why do you want to back up through an image file which is too large for handling with Fat32?
All files on a DVD are max 1GB and there are many free softwares to help you first get those files on your HD and then get them on a DVD Video Compliant form on a DVD-R/DVD+R through suitable DVD burning software. Nero is an excellent burning software.
I would suggest that you go to www.dvdrhelp.com
to get all necessary info, software links and guides to carry out your back up task.
Best of luck and happy viewing