How to get feedback on a movie script without the idea being plagarized?

Register your script with the Writers Guild of America - http://www.wga.org/subpage_register.aspx... It costs just $20 and you can do it completely online, by uploading your script. Having your script registered with the WGA protects your copyright and enables you to refer back to the registered copy on the date you put it out there to counter anyone else's claims that they may have created the story first. To get feedback do a search of Yahoo Groups in your area for filmmakers and put a posting for people to read and review your script.