Boot off the Knoppix CD/DVD. I use the cheat code: knoppix 2 dma vga=normal
At the root prompt, use cfdsik and create the sda4
cfdisk /dev/sda
Once that is done you should reboot to make sure the changes are applied to the partition table. Next format reiserfs on sda4.
mkreiserfs /dev/sda4
Now mount the original and the new root paritions:
mount /dev/sda3 /mnt/sda3
mount /dev/sda4 /mnt/sda4
Copy your current linux system to the new HD:
cp -Rp /mnt/sda1/* /mnt/sda4
Once that completes then edit the /mnt/sda4/etc/fstab file.
change / from pointing to /dev/sda3 to /dev/sda4
Then edit /mnt/sda3/boot/grub/menu.lst and copy the three or four lines that represent the normal boot entry for knoppix. Paste them to the end of the file and change the title. Also change the reference from (hd0,2) to (hd0,3) or /dev/sda3 to /dev/sda4.
Save the changes and unmount /mnt/sda3 & /mnt/sda4
Reboot and it should work.
I hope this helps.
James