Most Services can be turned off in Administrative Tools.
Let me clarify that just a bit, just to prevent any confusion. Most services can indeed be turned off in Administative Tools, but that does not mean most services should be turned off, since most services are essential for your computer to run. Should you need to disable services, that is one way to do it. Windows ships with some services on by default hat are not always necessary for a particular consumer, so it is not really an earth shattering recommendation that some services could be disabled. For instance XP ships with support for uninterruptable power supply support enabled by default. If you do not have a ups, then there is no need to have that service enabled.