How's this for a mea culpa? Last month, DreamWorks took out an ad in Variety quoting critics' preference for its Best Supporting Actress nominee, House of Sand and Fog's Shohreh Aghdashloo, over Renee Zellweger, from Miramax's Cold Mountain. When the Academy chastised DreamWorks for playing dirty (in an otherwise clean campaign season), the studio issued an apology. In the end, Zellweger won the Oscar, and DreamWorks, apparently, couldn't be happier: It recently bought an ad congratulating her for a ''richly deserved Oscar.'' Thoughtful, considering Zellweger voices a main character in DreamWorks' fall flick Shark Tale.