[johnwill]

Install a software firewall, and wait for applications to ask to access the Internet. You'll soon find out which one it is. I suggest ZoneAlarm, the free one is the short stack on the left, but it'll do what you need to find this problem.

I suspect you've installed a peer-to-peer sharing package at some point, and it's still sharing.

 

[johnwill]

You have some applications that are sharing your files, my advice is to try to find out what's loaded and kill it off. The applications that ZoneAlarm is blocking should be a clue where to start.