The Flood aren't really hard, not even on Legendary. Just get a Shotgun, a Sword or perhaps a Magnum (In Halo:CE because the Magnum in Halo 2 is not nearly as powerful as it's predecessor in Halo:CE)
Remember, in Halo 2, they won't get back up unless a infection form gets to them. Besides, it's really fun dancing with them (not polka mind you)