PARK CITY, Utah, Jan. 23, 2000 -- So, what's it like when you sell your movie at Sundance? Like this: You drive through the streets whooping, yelling, cranking up the stereo and tossing black Adidas ski hats to the unwashed (and un-picked-up) masses. The groovesters of "Groove" are, yes, grooving. A day after Sony Pictures Classic snapped up the low-budget slice-of-rave-life flick, the film's players were partying in the streets here this afternoon. And to hear one of its stars tell it -- this w