Pat Green will open for Vince Gill July 20 at Cheyenne Frontier Days in Cheyenne, Wyo. Also on the bill for the annual festival: Nickelback (July 19); The Guess Who (July 21); Kenny Chesney and Tracy Byrd (July 24); Huey Lewis and the News (July 25); Doobie Brothers and The Nitty Gritty Dirt Band (July 26); Travis Tritt and Asleep at the Wheel (July 27). 03/18/02