Idvd files usually are related to larger files, like movies or slideshows. So ctrl click (left click) on all of your movie files, and idvd projects and choose get info. Then you will be able to see how big all of these files are. I recently cleared off some 5 min. movies I had on there and was able to free up 7GB of space. Just back up your files to a dvd so you will always have them.