Sorry, I mean that a Windows hard drive should be read-only by Knoppix (this is the default). Knoppix can't write anything on a Windows partition safely. Some people have reported corrupt files and filesystem after a while. Also, Knoppix is best used as a live-CD/DVD only. Apparently there are problems with installed Knoppix and updating afterwards.

Windows of course recognizes Windows partitions safely, but doesn't recognize Linux partitions at all.