My computer is running noticably slower and the "unable to
view page" screen is appearing quite frequently ever since
a window started popping up proclaiming, "The system has
detected a conflict for IP address (assumably mine) with
the system having a hardware address of (some other set of
numbers). The interface has been disabled."

Have I been invaded by a worm or virus or hacker or any or
none of the above? And what do I do?

Thanks!
Robert