Stopping a Toddler From Hitting

How can I keep my 2-year-old daughter from "beating up" on her 10-month-old brother? She kicks him, punches him, bites him, screams at him, and whacks him with toys. It all began when he started crawling. This kind of thing goes on every day, several times a day. We've done everything we can think of to stop the behavior, but so far nothing seems to work. Do you have any suggestions or advice?