An alternative is removable media such as Zip drives and Jaz drives . They are a great for backing up files and transfering large amounts of data between computers. If you buy a zip drive, be sure to check which model you're getting. They should also come with all the necessary software for making your own CD's. If you just got to make your own CD's, buy one of these.
Some computers come with one installed.
DVD drives are fairly expensive because it is both a special reader and decoder. It can use both DVD data and Movie disks as well as regular data and audio CD's. CD-ROM drives only recognize CD's, not DVD's. Both will come with any software and drivers that you may need. DVD for G3 power books - click for info and price.