Your motherboard is the thing that looks like a Big Circuit board and is inside the tower of your system, its hard to miss. http://images.google.co.uk/images?client=firefox-a&rls=org.mozilla%3Aen-GB%3Aofficial_s&q=motherboard&hl=en&btnG=Search+Images
Lots of pics here. Good luck
chips
October 2005