In Dallas, Texas, ANTIQUES ROADSHOW host Mark L. Walberg and appraiser Stuart Whitehurst mine a rich vein of silver objects at the Dallas Museum of Art, looking for examples of 20th-century modernism. At the Dallas Convention Center, it's high noon when a guns-a-blazing, Western-themed painting by Saturday Evening Post illustrator William H.D. Koerner draws an estimate of $150,000.