1-To run mpowerplayer on your PC first install the latest Java Runtime Environment for your PC. If you dont have it download it from here
http://java.com/en/download/index.jsp

2-Download Mpowerplayer to your computer via internet. Mpowerplayer has different chioces, either you start it via the web (Java Webstart)
http://webstart.mpowerplayer.com/index.jnlp
or you can download an SDK kit from their website. After download you can unzipp and extract the package.And Open the file player.jar to start the mpowerplayer player
http://mpowerplayer.com/products-sdk.php