Every week, you have a new movie,'' enthuses Adam Beach, who is about to take his place as a Law & Order: SVU regular. On the NBC series' season 8 finale (May 22 at 10 p.m.), Beach's Chester Lake an insomniac detective of Native American descent who first appeared in an episode last January will become the unit's newest investigator. Also this month, the Canuck stars as a Sioux doctor in HBO's historical epic Bury My Heart at Wounded Knee (May 27 at 9 p.m.). But Beach, 34, who first caught fire as the troubled young man in the 1998 indie Smoke Signals and even sparked Oscar buzz as a soldier in the 2006 World War II epic Flags of Our Fathers, doesn't worry about being typecast. ''I understand that I can't play King Henry V or Nelson Mandela,'' says the Saulteaux Indian. One bonus: He didn't need to do any research for Wounded Knee. ''That part of history is embedded in all Native American people. It's like identifying who you are.''