XP servicepack2

can someone help me: an unsuccesful installation of Service pack 2 of
windows Xp caused a command (update.exe) to be executed automatically by the
system. I tried everything in order to prevent such program to be run (also
in the options for automatic uptade). As a consequence the system goes into
a sort of overload (the CPU is occupied at the rate of 100%). I tried also
to interrupt such event by the task manager panel ...but nothing happens.
The system appears very slow and it is impossible to work with it, thanks in
advance
luigi