Is your computer on? If so, it's doing all sorts of things that you don't realize are going on. For example, SOMETHING is keeping your Internet connection on, your printer connection alive, and so on and so forth. These are typically referred to as services.
However, for each good service, there are a bunch of useless ones that are probably switched on in your system's setup. One of the first things I had to do when I got my machine was shut off wireless configuration. Why did I shut it off? I don't have a wireless card...but system resources were being wasted looking for wireless devices!
Changing some of your services is one way to squeeze more power out of your computer. Any changes you make are reversible. You can access the list of services by going to Start Menu, selecting Control Panel, and selecting Administrative Tools.
What's that? How do you know what to shut off? Well, there is a site that someone has put together with a list of the services that exist, an explanation available on the following Web site:
Not necessarily a beginning user thing, but a good thing to check out for an intermediate to advanced user.