"I have a musical where the plot is all my idea, but was inspired by the music of famous artist. I know I have to be very careful approching the artist, but what I am worried about is the plot it self being taken by the artist, and spun in a different direction. So the person that inspired me could infact just change a few words around and change the title so it would be thiers. Hopfully this makes some sence and I would love any info on the subject."
Joe's already given you the link to register your play with, which you should obviously do. I'd still like to point out that anything you write is under copyright protection from the moment you write it.
As for someone stealing your work, there's at least two reasons why that probably won't happen.
It's a whole lot easier to simply buy it.
And to be frank, beginner/newbie scripts suck so bad you couldn't pay someone to take them. LOL. And I said this as someone whose having to rewrite all of his bad first drafts. Not that their concepts were bad, but my execution of them was. I simply needed proper instruction which I'm now getting.