Click on Start/Settings/Control/User Accounts & you'll see how easy it is for different user desktops to be setup.
Usually the Administrator has more rights than a restricted Member ie in terms of adding & removing programmes.
It really is very simple when you look at it.
Anti virus & Spyware would probably be best done by the Administrator - not fair to put the responsibility on the family members - they just want to play games etc.
Hope this helps