First; you don't go around just killing off processes; you disable them and then reboot.
Two kinds of thing are at issue here
In the former list, you can easily control what is or is not autostarted when you logon.
- programs set to autorun for you
- system services autostarted
The system services are seen Start->run->services.msc
but then you should have an idea of what's running and what is not necessary according to your useage