Hide data on cd or dvd

first compress the data which you want to hide using winrar , you will get a rar file.
now you rename the .rar file to .iso
now using nero burn it to a cd or dvd
after this you see the magic! you see the content of the cd empty

to retrive the data
make a iso image of that particular cd and rename it to .rar and extract the data using winrar

even you can add password for that rar file