Start Up Processes on XP

I just got a Dell laptop with XP installed. It is my first experience with XP. The computer runs much faster than my old Hewlit Packard on most things but on some of the Internet Forums it lags very badly. It shows CPU usage is 100% at times and is in the 90s most of the time with only AOL running. I notice there are 19 Processes running at Start UP? I am sure some of these are not necessary but I dont know which ones I can use End Process to stop. Is there a list of these processes and what they are intended to do? Can I stop them from starting in the first place. How do I clean this up? I can post the actual list of processes if desired?
Really need some help on this.
Marv