There is no such thing as a new idea.

   Wizards Hall Vs. Harry Potter


Wizards Hall was written by Jane Yolen in 1991.  It is a story about a young boy named Henry who goes to a school of wizards called Wizards Hall.  Yolen didn't receive much attention for this novel, nor did she win any awards.  Notoriety came to her novel only after J.K. Rowling published her first novel of Harry Potter, Harry Potter and the Sorcerer's Stone.  Yolen's response was this:

"I wrote a book called Wizard's Hall. And there's an awful lot of Wizard's Hall in it. I always tell people that if Ms. Rowling would like to cut me a very large check, I would cash it."

There's no doubt that many stories written will draw heavily on other ideas.  The important thing, is to make it our own, to add our own twist.  Rowling didn't copy off of Yolen, perhaps she had never even heard of her until her own book was published and Yolen responded with negativity.   Either way, Rowling took an idea, transformed it, added to it, and published it.  As long as you draw from a number of sources, bounce ideas off of numerous people, and create unique and new characters, you won't run into a problem of plagerism.  Sometimes your ideas will sound a lot like other peoples, but don't worry.  A lot of the best ideas were borrowed and adapted.

Creation is a beautiful thing.