I would personally replace the CD drive with a DVD, i'm not sure which portable you have, but check ebay, either way, it doesn't really matter which drive you get so long as you get a Slot or tray loading (again i don't know which model you have) Or you can boot it up via target disk mode, remove the hard drive if you have another mac laptop..
Let me know which model you have and ill find you a dvd drive.