Can I burn a CD ISO to DVD?

If the image is an ISO, most, if not all major commercial software can handle burning the image such as Nero or imgBurn on a PC or Toast or Disk Utitliy on a Mac.

As you are talking Fedora, you apparently can just Select DVD ISO image in file browser and and do a right mouse click to open "with CD/DVD Creator", the set your write speed. Full steps are here

As to the specifics of the question of fitting a CD image onto a larger DVD disk. Yes it works no problem, you just waste the remaining space.

Short Answer : YES

Long Answer : Technically isn't an iso image file burnable onto just about any type of optical media, even blu-ray? it just is kind of a waste, burning a cd image on a dvd

It shouldn't be that much different. But did you select a DVD project, or a CD project? They are different in Nero express. If you have started a DVD project, I don't think it should ask for a CD. I am not a pro with Nero, though :-) and fellow these steps

if you CAN use NERO. its the best you know.

open NERO BURNING ROM. (NOT NERO EXPRESS). 

click on ISO.

change nothing.

click on "OPEN"

select the ISO file, the file you want to burn to disc.

Or You any one of these buners http://iso.snoekonline.com/iso.htm

As long as the medium is writeable and has enough space for the ISO it can be done. However practically it does not make much sense.

Windows 7 allows direct writing of ISO. I personally use ImgBurn.