This should be in Mac OS forum, but at any rate:
Open System Prefs, open CD & DVD prefs, and select when a blank CD or DVD is inserted "ask what to do" or "Open Finder". If you have "Open iTunes" selected for blank CD media, and "Open iDvd" selected for blank DVD media, inserting blank media will not pop it up on desktop (assuming "show CDs, DVDs & iPod" is selected in Finder prefs), it will instead open up the assigned application.
Also check Finder>Prefs>Sidebar and make sure you have "Show removable Media" selected.
Hope that helps.