New Name for Multiple Personality Disorder

The names and classifications for mental disorders keep changing. What was formerly known as multiple personality disorder is now as dissociative identity disorder. Is that the same as what some people call a split personality? Or is that bi-polar disorder? This is so confusing! I guess this is why psychiatrists are the best people to deal with mental disorders.

What do I do if I know someone who has some sort of dissociative disorder? How can i help him or her get treatment? Who do I call? Will I have to call a hospital or a psychiatrist directly? What if the person refuses to get treatment?