authentication problem



i have a machine windows 2000 pro stand alone of active directory , and need
to perform updates, I add the anonymos rule in my ISA2000 server...but when i
try to update after click on "express button" in WUpdate page its show the
progress bar and send popups requering user and name..... y put again the
authenticated user for ISA Server....but doesn't work... in a seconds the
popup is showed again.
Thanks for your assistance....
.