to stop it from starting you need to stop the service from starting up at windows boot time
1: click start
2: on the right hand side, right click "Computer" and click manage
3: when computer management console opens click on the services and application tree
4: click services
5: scroll down to "Windows media player network sharing service"
6: right click and choose properties
7: change "Start Up Type" to disabled
8: click apply and ok then close all open windows and reboot TADA no more wmpns service