get final draft and save your script as a pdf before you send it out to people. getting a script as a word document is a pain in the ass and even hardcore amateurs won't accept it.
i hear movie magic screenwriter is good, too, but i've never used it, so i'm not vouching for it.
also, there are some macro programs that can format a script in microsoft word, but you'll still want to save it as a pdf before you send it to anyone.
just don't use word. unless you specifically don't want anyone in the industry to ever read it. i'm speaking from experience here. only pdf.