I doubt it is something as obvious as this, but just in case...
I recently upgraded from a CoreDuo Mac mini, to a Core2Duo Mac mini. The original Mac mini had a hated Matsushita made optical drive, the Core2Duo had a Pioneer optical drive. Both are being used to run Boot Camp and hence Windows Media Center 2005.
After moving my installed Windows environment to the new Mac mini, I noticed that the CD Text option was greyed out (it had been enabled on the CoreDuo). This was not because the Pioneer drive does not support CD Text, but because iTunes for Windows was still remembering the selection of the Matsushita drive which was no longer available to use. Once I told iTunes to select the Pioneer drive, the CD Text option became available again. This is done in the Advanced/Burning part of iTunes preferences.
iTunes for Mac seems to automatically select any optical drive that is available (unlike the Windows version).