Testing for CPU usage

I have a Del lnspiron with Windows Vista. I remember hearing(I think something ? like this)that one way to test to see if you might have a virus is to test for CPU usage. I've actually done this several times in the past but can't remember how to do it. I do remember it was only one or two steps at which point I got a little graph. Supposedly if the the usage was low(like under 10%)when I had no other programs running this meant that it was unlikely my computer was infected.

Can someone please remind of the steps I need to do to look at CPU usage?
Thanks.

 

Hold CTRL & SHIFT & ESC to open the task manager, and then either click on the "processes" tab and click on the "CPU" column to sort by hightest CPU usage, or go to the resources monitor tab and you can watch the graph there.

 

You can all so Press Alt+Ctrl+Delete as well to open task manager.