Then go and read "NIN Dazzles With Lasers, LEDs and Stealth Screens" at wired.com for the answers! Great pics too plus a video montage thing of clips from the tour.
ETA: Also, at the Moment Factory website you can see pictures and a video detailing the creation of the stealth screens on the LiTS tour. Go to Company, then Experience, then Live to find the video and pictures. Thank you to Troy and Michael for letting me know.
thanks cynicmuse