The processes you see in the Task Manager are actually currently running "services" and "programs." If you end those processes using task manager, it will close them, but they will just come back next time you reboot.
Instead, you need to eliminate them in a different way. You need to keep them from starting up in the first place.
To do this, you must check two things: Windows XP Services and Programs that startup with Windows XP. Tinker already gave a link dealing with Windows XP Services.
Windows XP Services
(1) Go to Start -> Control Panel -> Performance and Maintenance -> Administrative Tools -> Services
(2) You will see a long list of services.
(3) To make things easier you might want to click on the "Status" column heading so that you can see all the services that are "Started." Started means that they are currently running on your system.
(4) At this point you must decide which services you want (and can safely) disable.
Tinker already provided a good link for this area. However, I would also recommend another page on that site: http://www.blackviper.com/WinXP/service411.htm
That link will give you detailed information about what each service is, and, thus, let you decide if you can disable it.
(5) To disable a service do the following:
A. Right click on it and select "Properties."
B. Hit the "Stop" button.
C. Then on Startup type:, select Manual or Disabled to prevent it from starting back up the next time you reboot.
Disable Startup Items
In addition to the Windows XP services, there are certain programs that startup with your computer. Some of these programs must be disabled elsewhere because they are not services (they are just plain old programs).
(1) Go to Start -> Run -> type in "msconfig" and hit OK.
(2) Go to the [Startup] tab.
(3) Mostly likely, you will see a long list of stuff. However, in order to figure out what each one is, I recommend you visit this site: http://www.pacs-portal.co.uk/startup_pages/startup_all.php
Just use the "find" command in your browser to search for each one you see in msconfig.
(4) Once you have figured out which ones you think you don't need, just uncheck that item in msconfig.
(5) When your done, hit OK. There is no need to reboot at that time. However, the next time you reboot, the programs you unchecked will not startup with windows.
NOTE: You can use this msconfig solution as long as you want. Additionaly, you can also seek to eliminate the startup info from the registry permanently.
There are several ways to do this.
(1) Uninstall the program. If you found a program that you don't want on your system anyways, this is a good solution.
(2) Look inside the program for some setting that tells it to startup with the computer, and disable it. Usually, this will remove it from the registry.
(3) As a last resort, you can edit the registry itself.
The following page explains how to do this: http://www.pacs-portal.co.uk/startup_index.htm
Simply scroll down the page till you find the following section:
5) The System Registry - Windows 95/98/Me/NT/2000/XP
Using these two techniques, you should be able to eliminate a lot of stuff from starting up on your computer and running in the background.
P.S. From looking at your list of processes, I can tell what some of them are.
For example, taskmgr.exe is your Task Manager that you have open.
opera.exe is your Opera web browser (of course)
All the processes that start with N are some Norton product (Firewall or Antivirus perhaps?)
SiSoftware Sandra Standard gives you some tips on which services to disable also.
Run performace tune-up feature.
It will say that task schedular can be disabelled. I can not to do this one as it prevents my norton applications to show disabled when I thought I had enabled them to do live updates in the background.