I have ubuntu 6.06 available in cd and I would like to have its ISO file on my hard disk.
I want to know if I use the following command to make ISO file on my hard disk and if I write my ISO file on a cd , will my new cd be bootable or not?

I doubt that will be bootable. See this article:

http://www.troubleshooters.com/linux/coasterless.htm

Use the rawread script in that article to check the md5sum of the cd, to make the iso and to check the md5sum of the created iso to make sure it matches the cd md5sum. It's the most accurate tool I've found for generating an iso from a cd. A cd burned from an iso generated from rawread will be an exact sector by sector copy of the original cd which is what you need for the cd to be bootable; certain boot info must appear on certain sectors for a cd to be bootable. mkisofs will put all the data on the cd but not in the same place. The "dd" command will give you that sector by sector copy but you can run into other problems with dd that the rawread script corrects. The article explains it all much better than I can.

Here is a part of a tutorial on making an ISO from a Cd and the command to do it.

Make an iso image of a CD:

dd if=/dev/hdc of=/home/sam/mycd.iso bs=2048 conv=notrunc

CD sectors are 2048 bytes, so this copies sector for sector. The result will be a hard disk image file of the CD. You can use "chmod a+rwx mycd.iso" to make the image writable. You can mount the image with "mkdir /mnt/mycd", this line in fstab: "/home/sam/mycd.iso /mnt/mycd iso9660 rw,user,noauto 0 0", save fstab, "mount -o loop /mnt/mycd". Then the file system will be viewable as files and directories in the directory /mnt/mycd. You can edit the image as you wish, and the new file will be "/home/sam/mycd.iso" dd does not write to CD's. You need to use a burning utility, or the cdrdao command.

The full artical is at http://www.linuxquestions.org/linux/...ything_With_DD