Slow update

I have W2K server, Citrix Metaframe, Symantec Antivirus CE
8.0, HDSL for connect to internet. Any Windows update is a
big problem because it's take about 2-3 hours. Yesterday i
upgrade to SP4 and it take 24 hours !!!!!!!!!. Why is it
so slowly with any windows update? I have other W2k server
in network but it is fast, SP4 in 15-20 minutes. What can
i do to upgrade faster?
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Thanks for ideas.