Using your thumbs, slide the lower case away from you.
The lower case may stick in the front on a tab just above the center of the DVD drive. Be careful as you work the case off, or you may break the thin strip of plastic just above the drive.
If your G4 has a CD-RW or Combo drive, the pictures in the following steps will not exactly match your computer.
Before continuing, place a soft cloth on your work surface to rest the computer on. Turn the G4 over, making sure the DVD drive doesn't fall out. Place the computer on the cloth.