In your Start menu, right-click My Computer and select "Manage".
Expand "Services & Applications".
Open "Services". (Perhaps maximise the screen to better see what's going on.)
Right-click the Bonjour Service and select "Properties".
In the General tab, set the Startup type to "Automatic":
... and click OK.
Restart the PC and try opening iTunes again. Does it open without the Bonjour message this time?