I tend to be very careful using pcman, and rather do the basic administrative steps from the command line. This has been mentioned a number of times before, but here it goes:

First, open a terminal window and check what the Knoppix system thinks is the storage setup:

Code:
knoppix@Microknoppix:~$ fdisk -l

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x76692ca8

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1        1912    15357116   1c  Hidden W95 FAT32 (LBA)
/dev/sda2   *        1913       17112   122094000    7  HPFS/NTFS
/dev/sda3           17113       60801   350931892+   f  W95 Ext'd (LBA)
/dev/sda5           17113       60801   350931861    7  HPFS/NTFS

Disk /dev/sdb: 16.0 GB, 16001036288 bytes
32 heads, 63 sectors/track, 15501 cylinders
Units = cylinders of 2016 * 512 = 1032192 bytes
Disk identifier: 0x0ce14c25

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1       15501    15624976+   c  W95 FAT32 (LBA)
knoppix@Microknoppix:~$
Hopefully, you will see some Windows HPFS/NTFS partitions, like I did here. If you don't, you should go back to Windows disk administration and register carefully Windows' view of the system. And close fully down afterwards (cfr krishna.m's remarks). Here, /dev/sdb1 is the 16GB FAT-formatted USB stick I am running Knoppix from.

IF you see what you are looking for, then you could try a manual mount of the system. At this point, you could become superuser (root in Unixspeak), but it is safer to take on those privileges on a per command basis, by prefixing all commands with sudo.

Code:
knoppix@Microknoppix:~$ sudo mount -o ro -t ntfs /dev/sda5 /media/sda5
knoppix@Microknoppix:~$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sdb1             15609712   8291128   7318584  54% /mnt-system
tmpfs                  1048576         0   1048576   0% /ramdisk
/dev/cloop             8827264   8827264         0 100% /KNOPPIX
/dev/loop0             3691008   1733424   1770084  50% /KNOPPIX-DATA
unionfs                3691008   1733424   1770084  50% /UNIONFS
unionfs                3691008   1733424   1770084  50% /home
tmpfs                    10240        68     10172   1% /UNIONFS/var/run
tmpfs                    10240         0     10240   0% /UNIONFS/var/lock
tmpfs                   102400       104    102296   1% /UNIONFS/var/log
tmpfs                  1048576        12   1048564   1% /tmp
udev                     20480       440     20040   3% /dev
tmpfs                  1048576         4   1048572   1% /dev/shm
/dev/loop/1            3444972   1008304   2261668  31% /store/share
/dev/sda5            350931860     41768 350890092   1% /media/sda5
Here, I use the Unix mount, with the switches -o ro -t ntfs to mount a NTFS partition readonly. The mount point has to exist, /media/sda5 is automatically created by the system for you. The df command tells you how much space is left on each device (implicitly, what devices are in fact mounted), you can see the NTFS volume /dev/sda5 turned up with 350GB free.

Now, you can take backups and collect all sorts of statistics from that NTFS volume safely, because you have mounted it readonly. You can unmount it manually too, sudo umount /media/sda5 in my case, but it will be unmounted on system shutdown in any case, so it is not mandatory.