Excel Viewer 2003 updates fail - Error 25090 with Office Source En

[--J--]

I'm running WinXP Pro-SP2 with Office 2000 SP-3, but I also have Microsoft
Office Excel Viewer 2003 (11.8012.6412) SP1 installed.

Recently the Automatic Updates feature downloaded two new updates (KB917151
& KB918425) for me related to Excel Viewer 2003, which initialise 'OK' but at
the install stage they both 'Fail'. Other updates downloaded at the same
time all installed fine.

I have tried restarting the PC and retrying the installation, with the same
result.

I have tried manually downloading the updates
(office2003-KB917151-FullFile-ENU.exe &
office2003-KB918425-FullFile-ENU.exe), and they also fail to install, but at
least they give me an actual error message to work with, with both updates
giving this exact same response --

============================================
Microsoft Office Excel Viewer 2003
----------------------------------------
Error 25090. Office Setup encountered a problem with the Office Source
Engine, system error: -2147024894. Please open and look for "Office Source
Engine" for information on how to resolve this problem.
============================================

I then tried unzipping the update files manually to look for the information
described, but there were no document files in there to help - hence the
reason I've had to turn to the newsgroups.

I have checked in my Services (services.msc) that the Office Source Engine
service is set to Manual.

Any ideas?