Go to Start / Run and type MSCONFIG, and go to the Startup tab, this will list programs that start automatically, remove a tick from ones that you don't want.
To stop processes entirely you can go to Control Panel / Administrative Tools / Services this will list all services installed. Here you can start, stop or set any of them to manual.
Before messing about though I would not all running services and take a look here click here to see if any are essential.
One thing you should do though is get a copy of Adaware and Spyware Search & Destroy, because it's likely that some piece of malware is sapping your bandwidth