OMG, Is it Fremont Street? I think so. Blocks of it are covered by a screen of some sort over head and they have light shows and stuff- really neat.
Yeah, here is a link. I was amazed, it is in the older part I believe. It has shows on a very frequent schedule and you don't have to stop walking or anything. Kinda trippy.
http://www.vegas-dreaming.com/fremont.htm