Burning a ISO image to a CD or DVD with GNU/Linux is very easy indeed. The wodim command that replaced the old cdrecord software that used to be shipped with Linux is the standard application for performing these tasks. The -speed parameter sets the speed that the ISO image will be written to the DVD disc. Writing at a slower speed such as 8x is better than writing a large image at the maximum speed.
# wodim -eject -speed=8 -v FreeBSD-8.1-RELEASE-i386-dvd1.iso
If you wish to create a ISO image of a CDR to then burn to a new disc, this command will suffice.
dd if=/dev/sr0 bs=1 of=/home/neo/disc.iso
To create a ISO image of a folder, this command will perform this task.
$ genisoimage -J -l -o music.iso Music/
This is the resulting ISO image ready for burning to a CDR.
$ ls -hula music.iso -rw-r--r-- 1 neo neo 412M 21-04-12 07:30 pm music.iso
My older CD burning tutorial is here: http://www.securitronlinux.com/linux-configurations/#cdroast this is also a good resource for learning how to perform this task with the command-line.