PARTY TIME: The top rung of the record biz was on hand Oct. 19 in New York when the AMC Cancer Research Center honored MTV Networks chairman Tom Freston at its 20th Humanitarian Award Dinner. But it wasn't so much who was there as what they were wearing that made the banquet such a unusual event. Instead of giving a stuffy awards dinner, Freston turned the event into a costume ball, asking industry heavyweights to come dressed as their favorite hero. The results were revealing --to say the least. Capitol chairman Joe Smith came dressed as Magic Johnson, Giant Records president Irving Azoff came as Count Dracula, Geffen Records president Ed Rosenblatt came as . . . David Geffen, Virgin Records co-chief Jeff Ayeroff was the Grateful Dead's Pigpen, EMI chief Jim Fifield came as John Malkovich (from "Dangerous Liaisons"), Hollywood Records president Peter Paterno was Duke Snyder (in a Brooklyn Dodgers uniform from the Disney prop department), E-TV chief Lee Masters was Homer Simpson, A&M exec Wayne Isaak came as Jim Morrison (handcuffed to a rent-a-cop), Chrysalis publicity exec Frances Pennington was Twiggy, manager Michael Lippman was Mickey Mantle, while CBS Records chief Tommy Mottola came as . . . himself, wearing such a sleek silk suit that one industry wag quipped: "Maybe Tommy came as John Gotti." And what about Freston, whose dinner raised $1.1. million? The MTV chief came as his childhood hero . . . Jack Kerouac.