It is surprisingly easy to create .iso file in Linux. I have tested the method on Ubuntu Feisty and I am sure it works on other distro as well.
Open up terminal:
Assume that /dev/cdrom is the location of CD/DVD-ROM
sudo umount /dev/cdrom readcd dev=/dev/cdrom f=file.iso
If you want to mount your .iso file,
sudo mkdir /media/iso sudo modprobe loop sudo mount -t iso9660 -o loop file.iso /media/iso/
Sources: How to create Image (ISO) files from CD/DVD [Ubuntu Guide]