Creating an ISO Image under Linux from the command line is a really easy process. Fire up your favorite terminal and type the following:
dd if=/dev/cdrom of=<iso image name>
The if is for input file and the of for output file. There are lots of options for dd so check out the man page.
To mount the newly created image (as root) you can mount it as a normal device with the -o loop option:
mount -o loop <iso image name> /mnt/<dest dir>