If you want to burn CD images to CD usually you use the ISO format.
However, there are other formats containing raw date of an CD image.
These formats are NRG, IMG, CUE/BIN and MDF.
to convert these images to ISo you need to install software thats found in the universe and multiverse repository. These software programs are command line programms. If you're not comfortable with it, it's not for you.
To enable this repository navigate to [System] > [Administration] > [Software Sources] on the applications menu.
Enter your superuser password.
The software sources window should appear. Enable the "Community maintained open source software (universe)" and "Software restricted by copyright or legal issues (multiverse)" option.
Now you have the universe/multiverse repositories enabled!
to install the software needed for the conversion install these packages:
bchunk (CUE/BIN to ISO),
ccd2iso (IMG to ISO),
mdf2iso (MDF to ISO),
nrg2iso (NRG to ISO),
so open a terminal and type:
sudo apt-get install bchunk ccd2iso mdf2iso nrg2iso
enter your password and there you go.
Here's what to do to convert from...
open a terminal, go to the folder where the file is located (using the cd command) and type one of the following commands:
IMG to ISO: ccd2iso filename.img filename.iso
MDF to ISO: mdf2iso filename.mdf filename.iso
NRG to ISO: nrg2iso filename.nrg filename.iso
CUE/BIN to ISO: bchunk filename.bin filename.cue filename.iso