You're telling us almost nothing. What type of partitons are you using? If they are NTFS (the default for XP) then you simply cannot write to them with Linux. If they are FAT then you can, but Knoppix defaults to read-only access for safety and you have to over ride this to write to them (with the mount command from a shell prompt or with he actions ... submenu if right clicking on a partition icon). All documented in the wiki and in these forums many times.