The warning is about using 4x media in unpatched 2x drives - this could damage the drive, media, or both.
Make sure you go to Apple's support page and download the firmware update for your SuperDrive. Do this BEFORE attempting to use 4x media in your 2x drive.
Be aware, however, that 4x media will actually run at 1x speeds in a 2x drive once patched (hope that made sense... so many x's). For best results, use only 2x media in your 2x drive (it'll run at full 2x speed).
Oh, and stick to "-" media. The "+" media is a different format and not compatible with your drive.