You appear to be describing two problems:
1. You cannot write to your RH file system and
2. You can only see Desktop directory in your RH filesystem

For 1, it could be that your RH file system has been mounted read only, check with the mount command.

If it's been mounted read only it will contain the word ro in brackets (possibly among other comma separated words).

If that is the case, remount the RH file system rw.

I don't know enough to comment on why KNOPPIX would choose to mount a Linux filesystem read only, but I recommend you find out why before remounting it rw.

For 2, are you sure that the RH filesystem that has been mounted by KNOPPIX is the right one?

Cheers
Dan