it was nothing unusual. For years, layers of television history have been waiting to be unearthed: recordings of vintage shows, hundreds of which have fallen out of sight. Some have easily been found; some have been entombed in the most unlikely places. Others might never be retrieved. Show-biz archaeologists have gone from coast to coast to uncover lost shows: to the basement of a dentist's house in Alexandria, Va.; to a condemned watch-company building in Illinois; to a garage sale in Westchester County; to Dumpsters outside TV stations across the country. Their efforts don't get much attention, especially compared with high-profile, well-funded campaigns to preserve films, championed by the likes of Jodie Foster and Martin Scorsese. But, according to archivists, TV preservation is just as urgent. Patrick Loughney, head of the moving image section of the Library of Congress, cited an alarming conclusion reached by his institution's 1997 study of TV