How to kill processes in Windows 7 Ultimate (PERMANENTLY)?

I've been using my Toshiba NB200 for already a year, and I'm starting to experience lags, and slow response from my Laptop. My friend suggested to kill all "unwanted" processes. After I have done it, my laptop starts to get faster, which is ok, but every time I shutdown/restart/log off, every single process I killed before, returns back, how can I kill these "unwanted" processes PERMANENTLY without harming or deleting important files in my laptop?