Does Knoppix's desktop show an icon for the partition? If so clicking on it should open it (in read only mode, for file recovery). If the desktop doesn't show the partition icon then yes, the partition might be damaged beyond Knoppix's ability to open it. Or it could be that the partition is fine, but the partition table is mucked up (unfortunately, not uncommon with Windows). If you don't have a partition icon, try looking at the man pages for testdisk and gpart. You may want to use Google for aditional documentation as well. Either of the commands has the ability to examine the disk and try to repair a bad partition table. There is not much they can do though if the partition itself is destroyed.