All I can say is that I tried PC Guard when I first got Virginmedia as it was free and had nothing but problems with my PC crashing all the time. In the end I took it off and bought another anti virus and when that subscription ended I bought Norton Internet Security 2009 and have had no problems. Best thing is NIS 2009 does not hog your system resources.
My advice would be if you can buy Norton Internet Security 2009 asap as you can get a 3 computer license pretty cheap, useful if you have more than 1 computer, you can upgrade to Norton Internet Security 2010 when it is released.