Hi there, I can shed some light on this;
If you have a the older style Cinema Display (pre-Thunderbolt) and the status light gives 3 flashes then a pause; it's not going to work.
That display only accepts a digital signals. You need a separate breakout box to convert the analogue signals from the Pi to digital in order to work with this display.
These devices do exist, but they're pricey. I saw someone use one to get an Xbox to work with this display. I believe a company called Blackmagic make just such a device.
The newer Thunderbolt displays will accept analogue signals, but they cost 32 times more than the computer you're going to be running it with.