I'm trying to use a Knoppix Live CD to make backup copies of a Windows NTFS partition using dd. I need a bit of help. I'm pretty familiar with Unix, but am new to Linux.

The background of my problem is as follows: When installing Windows on a single hard drive, my normal procedure is to create one partition for the operating system, and a second extended NTFS partition called DATA. Normally, I use a bootable Norton Ghost disk to make backup images of the operating system partition as I proceed through the installation process. I store the ghost images of the operating system partition on the DATA partition. So, for example, I'll install windows XP on the operating system partition and make an image called XP0, which I store on the DATA partition. Next, I'll install all the hardware drivers and make an image called XP1. Then I'll install service pack 2 and make image XP2. Next I install windows updates and create image XP3, and so forth. I do this in case, for example, a windows update hoses the operating system, I can restore image XP2 and move forward, without reinstalling everything from scratch.

I'm trying to accomplish the same process using dd from a Knoppix Live CD. I created the CD from this iso:

KNOPPIX_V6.0-ADRIANE_V1.1CD-2009-01-27-EN.iso

My hard drive is a Western Digital 250 GB SATA drive. My motherboard is an MSI K9N2 SLI Platinum. I've installed Windows XP and created the NTFS extended partition called DATA. Here's what I'm doing to try to make the first backup image:

1) Boot off Knoppix Live CD
2) Choose option 9 (shell) to get a command prompt
3) Gain SuperUser access by typing:
sudo -s
4) I type
ls /mnt
and I deduce that the operating system partition is /dev/sda1 and the extended partition is /dev/sda5.
5) I try this command:
dd if=/dev/sda1 of=/dev/sda5/xp0.dat
6) I get this error:
dd: opening "/dev/sda5/xp0.dat" not a directory

Do I need to mount /dev/sda5 first? Or do I mount /dev/sda1? Or both? Or am I doing something else stupid?

Any help would be greatly appreciated.