Not sure about the Norton….what happens when you try to get into MSN with Norton running ?
Probably the reason why your PC was slowing on tinternet was becaue your music software was connected too [you don’t necessarily have to open the programme for it to do it – it could be in your start-up to automatically connect/search/upgrade, etc].
You need a good firewall which will block anything going out on tinternet that you don’t want.