I am presuming you have windows XP.
Go to 'Start' Click 'Run' then type into the box 'msconfig' without the '. OK the button and you will get the 'System Configuration Utility'. At the top right you will see the tab 'Startup' Click on this, run down the list and you should see the name 'Realsched', untick this, Click the 'Apply' button, then the 'Close' button, you will then get a box telling you to restart your computer, do this and you should find that Real Player will stop. When your computer start's up a box will appear saying something like, 'System Configuration Utility, You have used this utility to change how windows starts up......' tick the box that says somthing like 'dont show this message at start up' and Click 'OK'.