Don't try mounting your NTFS partition read-write and writing to it using the NTFS drivers that come with the kernel. Data corruption could result. Mounting your NTFS partition read-only is perfectly safe, however.

In order to write to it, you can use the Captive project's software, to which there's a handy link in the Knoppix menu on the K menu (Knoppix > Utilities > Captive NTFS) or on the panel. It uses binaries from Windows XP in order to (safely) mount NTFS partitions in read-write mode.

Clicking the "Captive NTFS" menu entry will bring up a GUI-based installer, named "captive-install-acquire," that will allow you to a) scan a local partition for the needed files; b) specify where the files are, including network shares; or c) download them from Microsoft. It will then copy the files (cdfs.sys, fastfat.sys, ntfs.sys and ntoskrnl.exe) to /var/lib/captive and set up the program. At the end, it will give you a short explanation of how to mount your NTFS partition; e.g. as root, type the command

mount captive-ntfs /dev/hda1 /mnt/hda1

(use whatever mountpoint you desire).

You should read the man page for captive-install-acquire for information on how to run it from the bash prompt (i.e. without the GUI).

And you should definitely browse through the Captive user support/bug list mailing list archives before you start using it. It'll provide answers to quite a few questions.

My experience with it is that a) it's better to use partitions mounted with it from the bash prompt, because using it with graphical file managers like Konqueror eats up a ton of memory; b) it's somewhat flaky; and c) it's much more reliable at creating files than it is at editing existing files. Plus, the data isn't permanently saved until you unmount the partition.