It's official: NBC's Medium is a bona fide hit. Monday's second episode won its time slot with 16.3 million viewers. Even more impressive, the Patricia Arquette drama retained all of its first-week audience. Fox's 24, meanwhile, had another good day, averaging a potent 12.6 million viewers for its second round of back-to-back episodes. And 2.3 million D-list gawkers turned out for the fourth-season premiere of The Surreal Life Sunday, making it VH1's highest-rated program in four years.