I've had this PC for 4 years now, and I've always been having this same problem. For some reason, roughly once every minute, my internet connection will freeze, then resume. Not long enough to disconnect me from the internet, but long enough to cause a very bad lag spike in my games. I do a lot of online gaming and streaming videos, and this issue has became a real problem. Over the years, I've changed my Antivirus (firewall) Network adapter and router. No one else in the house has this issue, even when I am the only one on the network. I also have moved my xbox next to my computer to test this issue in case it's a location problem, but that still connects fine. I've also had laptops up in this room that also do not experience this problem. The only things I have kept consistent is the operating system (Vista), Processor, ISP and motherboard.
I'm not looking for a perfect solution, some rough estimate into the cause of this problem would suffice. But anything you can offer would be appreciated. It's just started to become unbearable.