Select the 20 photos in iPhoto and use the File ➙ Export ➙ File Export menu option. If you want the orignal files to be exported select Format=Original. If you want the latest edited version select Format=JPEG.
Save the files to a folder on the Desktop. Insert a CD into the optical drive and drag the folder onto the disk's icon on the Desktop. Then drag the disk to the Trash bin in the Dock to burn it.
Burning a disc from inside iPhoto creates a mini iPhoto library on the disk that can only be used by a Mac with iPhoto.
Also your topic title has nothing to do with the problem you're having. Next time make the title brief and relavant to the problem so others know whether to enter the topic or not.