Automatic Updates and service packs

According to
http://v5.windowsupdate.microsoft.co....aspx?ln=en-us
Automatic Updates installs "high priority updates". The matrix at the bottom
of the web page seems to indicate that this includes service packs.

My experience is that service packs aren't installed automatically, even if
they are classified as high priority/critical in Windows Update (.NET
Framework SP1, Internet Explorer 6 SP1).

Is this by design, or is there anything I can do to enable automatic
distribution of service packs as well? We are running Windows 2000
Professional SP4 - and the end users do NOT have administrative privileges.
Might this be the culprit?

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Jørn-Morten Innselset