There's not much chance of anything in Windows 98SE that isn't circumventable fairly easily. About the best you can do is install the writing software somewhere out of the way, don't install packet writing software, and delete the shortcuts for the writing software from the Start Menu. Even then, another user can simply install new writing software from CD.
About the only thought that comes to mind is to put a dual pole keyswitch in the power lead (one pole in the 5V line, the other pole in the 12V line) to the CD-RW drive and physically secure the case from opening.
On Windows 2000 or XP you could achieve this fairly easily.