How can I block Java updates, network-wide?
To disable the auto-update notification you should be able to set the dword value at HKLM\SOFTWARE\JavaSoft\Java Update\Policy\EnableJavaUpdate to 0 and HKLM\SOFTWARE\JavaSoft\Java Update\Policy\NotifyInstall to 0.
Here is a fragment from on of my startup scripts.
Option Explicit
Dim oShell
Set oShell = WScript.CreateObject("WScript.Shell")
DisableJavaUpdateNotification()
Function DisableJavaUpdateNotification
Dim Key,Value
Key="HKLM\SOFTWARE\JavaSoft\Java Update\Policy\EnableJavaUpdate"
Value="0"
oShell.RegWrite Key,Value,"REG_DWORD"
Key="HKLM\SOFTWARE\JavaSoft\Java Update\Policy\NotifyInstall"
Value="0"
oShell.RegWrite Key,Value,"REG_DWORD"
End Function