SAN JOSECity to host musical half-marathonAlan GathrightThursday, August 25, 2005City officials plan an October 2006 "rock 'n' roll" half-marathon and hope to attract 65,000 runners, walkers and spectators downtown and pump $12 million into the local economy. The 13.1-mile race will feature bands and cheering squads every mile. It is based on successful "musical marathons'' that promoter Elite Racing Inc. has held in San Diego, Phoenix, Nashville and Virginia Beach, Va.The race in San Jose on Oct. 8, 2006, will cap a two-day health and fitness exposition and cheerleading competition. A post-ra