Gromit801 from Metacafe has a very good comment about this video:
Marine Sergeant Carlos Hathcock actually did just this. His story has been what all of these sniper vs sniper stories have been based.
His book, Sniper, is the account of his tours in Vietnam as a USMC Sniper. He was so successful, that the VC put a price on his head, and sent one of their best after him. After several days of hide and seek, Hathcock noticed a flash of light, sighted on it and fired. His round took the VC sniper through the scope, and ultimately the head. The flash of light, was the sun reflecting off of the VC’s scope, miliseconds before he was going to pull the trigger on Hathcock.