ABC tried a new tactic Thursday to boost its ratings at 10:00 p.m.: It ran a "supersized" version of its hit, Grey's Anatomy. True to form, Grey'spulled the highest ratings of the night at 9:00 p.m., scoring a 10.5 rating and a 19 share, narrowly outdrawing CBS's CSI: Crime Scene Investigation, which wound up with a 9.9/18. The network also allowed Grey'sto overflow into the 10:00 p.m. hour for ten minutes. It hardly seemed to help. The 50-minute version of Primetime, which followed (and which has not been seen since last September), together with the ten minutes of Grey'sproduced only a 5.6/10 -- about half the audience that Barbara Walters drew for a clips special one week ago in the same slot. NBC once again took the lead at 10:00 p.m., with E.R.drawing a 7.9/15, edging out CBS's Shark, which posted a 7.5/19. Otherwise, ratings saw a typical Thanksgivings Day drop overall, with CBS winning in overall households with an 8.2/15 average, followed by ABC with a 7.1/13. NBC placed third with a 6.9/13, while Fox trailed with a 4.5.8.