mgon23
No, this does not work like this.
The Intensity Shuttle does not turn your iMac into a Cinema display.
On the other hand you could use the iMac with our Media Express software in conjunction with the Intensity Extreme to "capture" your game play footage (over Component only), but the Media Express window is not full screen and this is not really what you are looking for.
Sorry it's not the answer you're looking for, but I hope that helps.