Not so difficult to write to a partition so long as it is a Linux format ,FAT or FAT 32.
NTFS is a different kettle of fish and probably shouldn't be written to from Linux until the utilities for doing this get better.
To mount a drive from desktop, just click the icon for a drive. This defaults to read-only.
To mount as read-write, right-click a mounted drive, then select "Actions" then "Change read/write mode".
To unmount, right click the drive icon and choose "Unmount".
Well recommended by me for tips and ways of doing things in Knoppix is "Knoppix, pocket reference" from O'Reilly, which I carry around everywhere to help fix Windows systems.
Happy hunting