I watched a film years ago when I was young and no one seems to know which film I mean and I am starting to think I dreamt of it or something. Its about a young boy who somehow finds the house of a rich guy who is out of town and manages to convince everyone that he is that guy. He then has parties etc and spends all this money, in the end I remember him throwing a big party but in the end everyone finds out he isn't the guy he says he is. Can anyone help?

"Blank Check" is similar to that, maybe that's what you're thinking of?