To lure even more viewers to its NFL games, Fox has enlisted such semi-buff stars as Melrose Place's Thomas Calabro, Beverly Hills, 90210's Jennie Garth, and Living Single's Erika Alexander and Kim Coles to do 10-second promos that promise ''same game new attitude.'' What's in it for the stars? ''We're thinking about having a celebrity skybox at every game,'' says Fox executive vice president of marketing Tracy Dolgin. ''It could be the new thing like being at the Knicks game.'' But with all the football fans involved, the scrimmage for seats may be better than the action on the field. ''I worked out a good deal,'' says Calabro. ''I get box seats to every game.'' Not so fast, says Dolgin: ''If he thinks he's going every week, we've got a problem.''