Some people think that with version 5.3.1 it is safe to write to NTFS with Knoppix. I'm not yet convinced. In the past many partitions have been badly corrupted by people using tools in Knoppix to write to NTFS (and people thought it was safe then too). So I'm not going to walk you through the process of making the partition writable, although I expect that someone else will come along who will. I suggest instead that you connect two computers across a network and run an FTP server on the destination system, then use Konquror on the Knoppix system as an FTP client. Alternately you could use a FAT formatted flash drive, or if the contents of the external drive are not important to you, format it as FAT32 and then transfer files to it.