Hit win + R and type services.msc and hit Enter. From here find the services and change the settings from automatic to manual. Also type in Windows Search autostart and check what programs are in that folder, remove the ones you don't want to run when your computer is starting up.
Go and download Process Hacker from here. It is a better Task-Manager. You can then just kill the processes you don't want or stop the services. Be careful not to stop some important services or processes which are needed for your computer to run normally.
Download Autoruns from here. You can see more services and stop them from auto running on your PC.
Open iTunes and the software manager and check in the options. Good programs give you the option to turn off process when not in use.
Advice: Upgrade from Windows XP to Windows 7, cause Microsoft won`t be supporting XP anymore.