I keep saying this every time someone posts anything about partitioning having learned the lesson myself the hard way. If you are going to repartition your drive for any reason, take advantage of the opportunity & create a separate partition for your data.. Never keep your data on the same partition as your operating system; one major crash & your data is history. With Linux you have a choice, either create a separate /home partition or just use a separate data partition & symlink to it from your /home.
For partitioning an existing drive, cfdisk is easy but can be destructive, parted & Qtparted can usually make partitions without losing any data.
BUT, parted (and hence QTparted since it is just a gui frontend for parted) seems to have problems with the knoppix/ext3 filesystem so it may not work (search these forms for 'parted'). If all else fails, linux fdisk can partition the drive but will probably trash data.
With any of them, run from the CD; you cannot partition a drive while it is being used.