Sandra Bullock, they say, is trying to harden her image. If so, she has a ways to go. "28 Days" is only marginally harsher than her last several women-in-trouble movies whether she be a robber on the run, a modern witch, an ex-prom queen brought low or an irresponsible drunk (twice now). Here, she takes the same route that Michael Keaton did in "Clean and Sober," which followed pretty much the same formula of a character facing inner demons. Bullock is a party girl who, after trashing the wedding of her sister (Elizabeth Perkins), is given a choice: 28 days in rehab or jail. But while the film overall offers little that's new, it does boast a few twists, and Bullock lovers will have a good time. Besides, it's always good to see a film where a woman character is forced to save herself instead of looking around for a prince, charming or otherwise.