when I try to open hard-disk partition of Debian in my system from a live CD, it says permission denied. What should I do to access it?

Which live CD are you using, and what's your user id (type id in a console window - the numeric id will be the most useful)? What type is the Debian partition, and what are the permissions on it? Is the partition actually mounted (does it appear in the output from df)?

I'm using debian(kde,amd64) live cd. In the installed debian, permissions are : 'owner'-r&rw, 'others' and 'group' -read ony; it's ext3. In live cd, it's automatic login. User id for installed linux is 'rajan'. THe partition is shown as 'Unmounted hard-disk volume' in properties ; it doesn't apper in df either.

Right - I've not used the debian live disk before, but the disk will need to be mounted before you can access it. In Knoppix, you mount the disk just by clicking on its desktop icon, but if this doesn't work, you may need to open a terminal window to do it. Mounting usually has to be done by root, but most live disks will allow you to become root without a password:
/mnt is commonly provided as a temporary mount point (though you can use another directory). The *** has to be replaced by the identifier of your disk, which could be:

hda1 (first partition on the primary IDE drive, IDE socket 1)
hdd2 (second partition on the secondary drive, IDE socket 2)
sda4 (fourth partition on the first SCSI, SATA or USB drive)

... and so on. If you can't see the identifier displayed anywhere, after becoming root enter fdisk -l. This will show all the partitions on all your "fixed disks", with the identifier in the first column.

Thank you very much for your help.
I got the identifier as hda(only one partition). But when I type the code in Konsole, it says 'you must specify the file system type'.

Sorry, I've just realised that I typed the mount command the wrong way around (how embarrassing). It should have been:
If you do need to specify the filesystem still, it is most likely to be ext2, ext3 or reiserfs if it's a Linux filesystem. You use a -t flag to pass it to mount, for example:
... and you need the 1 after it, even if there's only one partition.

Rob

Edited to add: Just found this. You should be able to get the file system type by running the following as root:

That worked. Thanks a lot.