This has nothing to do with Knoppix or Linux but I hope it will help you.
I had a similar problem with Windows 2000. The hard drive was broken but I bought a new hard drive,opened the box, connected the new drive as master and the broken drive as secondary master, installed win2000 on the new drive. Then I was able to copy files to the new drive.
If you cannot reach all files on the broken harddisk, try to make a windows backup of a whole partition and then copy the whole backup to the new drive. For some reason the backup could save files you otherwise could not see or save.