Windows 2000 Professional Upgrade to SP4

I have tried three things to update a current installation of Windows 2000
Pro. None succeed.

(1) Download SP3 and do install from downloaded file. When I do this, the
exe file explodes to a C:\?? directory that I cannot find. It does not begin
any installation process after exploding. It just terminates without any
message.

(2) Attempt an update of SP4 directly from Microsoft. In this case the
files download. Within 3 seconds after download, it reports a successful
upgrade.

(3) I reinstalled Windows 2000 Professional from original CD. Everything
goes smoothly when replacing original installation. After the reinstall, I
perform (1) or (2) above and get same results. After this re-installation,
it doeshappily upgrade with all Critical updates at Microsoft site except for
SP4 express.

What can I do to update without having to reformat hard disk and starting
over?? Need upgrade to install Office 2003.