A process and a program are different. A program may envelop or spawn a
number of processes and some processes (most notably svchost) will be an
umbrella under which several activities are running.
I think what you are looking for is something else. A number of
commercially packaged computers have a bazillion unnecessary programs that
are set to start when the system starts. They like to install their own
"management consoles" and "update notifiers", many of which are not necessary
for the correct functioning of your system. A program can start with
Windows by being placed in the run key(s) in the registry, in the startup
group on the start menu, or by running as a service. While an experienced
user may make changes to the run key(s) in the registry and disable services
in the services console, there are some serious (and sometimes unrecoverable)
consequences of making a mistake. A safer way is to use your Add/Remove
programs applet in your control panel (or type appwiz.cpl after going to
start > run) to view installed applications and uninstall things you don't
want/need. But be careful--if they came pre-installed, you may not be able
to re-install them if you change your mind without completely wiping your
system and restoring it to its from-the-factory condition.
Some programs that you may want to keep (such as Acrobat Reader or Real
Player--which I refuse to allow on my system), run an applet at startup that
places an icon in the system tray and runs an "assistant" that detects
available updates or attempts to open applications that might use the
program. You can usually uncheck a box that says "start with Windows" or
"load at startup" or something like that by going into the properties of the
program (right click on the icon and select "options" if available or
"properties".
There are websites that may help you to understand XP services and even make
suggestions for what is (and is not) essential. Use with care. One of them
is TheElderGeek
http://www.theeldergeek.com/services_guide.htm. While there
is a lot of good information, there is also some that I'm leery of. It's one
of those caveat emptor situations.