boot cd linux HOWTO?

i have linux bootable cd.
I want similar bootalbe cd with some chnage in the disk. i.e, some file from the old cd has to replaced in newer one.

how do i do it?

A simple and straight answer would be:

dd if=/dev/cdrom of=/tmp/bigfile.iso # dump the CD
losetup /dev/loop0 /tmp/bigfile.iso ; mount /dev/loop0 /cdrom # mount with RW

From there u can change anything, and then burn it back to a new cd...

mount -o loop,rw whatever.iso /mnt/cdrom
cd /mnt/cdrom
touch a

it says readonly fs.
but when i do mount it say its rw.

Same with your solution too

here is the output of mount with your solution

a/dev/hda2 on / type ext3 (rw,errors=remount-ro)
proc on /proc type proc (rw)
/sys on /sys type sysfs (rw)
varrun on /var/run type tmpfs (rw)
varlock on /var/lock type tmpfs (rw)
procbususb on /proc/bus/usb type usbfs (rw)
udev on /dev type tmpfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
devshm on /dev/shm type tmpfs (rw)
lrm on /lib/modules/2.6.15-23-386/volatile type tmpfs (rw)
/dev/hda6 on /home type ext3 (rw)
/dev/hda1 on /media/hda1 type ntfs (rw)
/dev/hda7 on /media/hda7 type vfat (rw)
/dev/hda5 on /tmp type ext3 (rw)
/dev/loop0 on /media/cdrom0 type iso9660 (rw)

thats weird, look at the whatever.iso 's file permissions and change if necessary then remount and try again, i did that many times without pb (modifying some rpms of some distrib.)