As mentioned before it's almost impossible to protect a CD so that it can't be copied. In fact I don't think I've ever come across one that can't be.
You don't say what type of files you intend to burn on to your cd/dvd but there are some steps you can take to make your CD not worth copying. If you have lots of picture files for example you could compress them so that thay are just about ok to view on a pc but look terrible when printed. The same thing goes if you have some sound files on your CD. Use a low bit rate so they sound poor when copied or listend to on a Hi Fi. You could advise your potential clients that your CD is a demo only and the quality of any original will be much improved.
Even the latest CDs, such as Life for Rent by Dido, which cannot be copied on a PC system can, in fact, be copied by those determined enough to do so.
I'm obviously not going to reveal how it is possible (and it certainly isn't using rocket science according to my information), but merely emphasising that unfortunately it is something that cannot be achieved by you with present methods.
Audio CDs use reflective and non-reflective "bumps" for the laser to read - a CD-R changes the reflectivity of the upper dye layer's surface to non-reflective as required; as the lower surface has full reflectivity, it pinpoints the reason for the "burning" of a CD-R or CD-RW disk.
This has nothing whatsoever to do with copyrighting disks...:-)