A local teen-ager has a big night planned. An 18-year-old Milton man, who's about to perform at what's best known as the Grand Ole Opry in Nashville, admits to being a little nervous. After little more than three years of singing and playing the guitar, Zac Matthews has earned the right to compete against four other finalists in the 32nd Annual Texaco Country Music Showdown. Despite wins at both state and regional competitions, Matthews says the toughest test was the first, during last summer's Rock County 4-H Fair. And this young man appears pretty impressed with the other finalists, and not just because he's the only guy. Most important he says will be showing the crowd what he can do. The winner Thursday night takes home a $100,000 prize.