Needed by Windows. They handle about everything in Windows, from logging in to networking to sound to security.
If it's forcibly shut down, either it will blue screen, or no sounds or no internet.
One cause of Windows being laggy is here:
http://www.sgforums.com/?action=thread_display&thread_id=254614Make sure that svchost is in C:\Windows\system32 folder, not any other folders. Any others, it's a virus and is usually a bad one.
Another tutorial about svchost:
http://www.sgforums.com/?action=thread_display&thread_id=221147If you are using XP Home, you have no Tasklist.
You can download one copy here:
http://www.computerhope.com/download/winxp/tasklist.exe