Preview Change is a useful application which allows you to change file type association to either plan text ( opens with notepad, Media File ( opens with Windows Media Player or set it to none.
This is pretty much useful when it comes to preview of files using Windows Explorer or when you want to see thumbnails. Infact opening an INI file with notepad is better then anything else.
Apart from this you can also dee details of some file extension so you understand a bit of what you are changing. So dont just go and change PPt to open with notepad. Find more details and download from Win Help Online