PARTY ON: Whether it’s the impact of the economy or another reason, there will be far fewer parties during New York Fashion Week next month. Alexander Wang and Marc Jacobs have nixed plans for their usual postshow parties, and Calvin Klein Inc., which is holding shows for both its women’s wear and men’s wear in New York this season, also will forego its traditional postshow party or dinner. But fashion revelers won’t have to completely give up on the good times. Diane von Furstenberg, who is scheduled to show her fall collection on Feb. 15, plans to have her traditional postshow dinner for her friends and family at her studio. On Feb.17, Giorgio Armani will be in town to host a cocktail reception to celebrate the opening of his Fifth Avenue megaflagship, and Narciso Rodriguez, whose show is scheduled later that evening, will be hosting his typically casual dinner for friends, family and editors.