this computer is a secondary computer sharing a modem of another computer which is protected with avg free.i tried to load avg on this system but it said i need an upgrade or somethin to get protection. also am i right when they say only one computer per household?i also tried to load a norton trial one and it said basically the same thing.is there an older version of these versions to cover an xp home edition[this is an ex office computer and my dad also refers to it as an windows xp proffessional]can anybody help me?nicole