go to my computer and right click, select properties and then the hardware tab, go into device manager and find your cd rom drive, right click on it and select disable.
your cd rom drive will not work unless you enable it, hopfully the other ppl using the pc and too good with pc's to figure it out. if they are and they know there way around a computer, you can set up user accounts and make it so they are just a user and dont have admin rights, this way they cant change it even if they know where to look.