The easiest way to type in Hindi is through a word processor that has been designed especially for this type of job. For example, the Hindi version of Shakti Office allows you to type in English and then, based on a built-in module, the whole text is automatically converter. Of course, the software offers direct Hindi typing through its main interface. You can read more about it using the following URL: http://www.shaktioffice.in/product/product.html
Additionally, you can browse other Hindy Typing applications using the link in the Kolappan's answer.