You can configure Automatic Updates in the Windows 2000 Service Pack 3 Control Panel.
In both Windows 2000 and Windows XP, you can use the registry to disable Automatic Updates:
1. Copy / Paste the following to a AUOFF.REG file:
REGEDIT4
\[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update\]
"AUOptions"=dword:00000001
"AUState"=dword:00000007
2. Run Regedit /s <path>\AUOFF.REG
NOTE: See tip 4373 » How do I configure the Automatic Updates features in Windows XP?
NOTE: AUOptions can have the following additional values:
"AUOptions"=dword:00000002 - Notify me before downloading any updates and notify me again before installing them on my computer.
"AUOptions"=dword:00000003 - - Download the updates automatically and notify me when they are ready to be installed.
"AUOptions"=dword:00000004 - Automatically download the updates, and install them on the schedule that I specify.