I don't want to confuse things with alternate instructions so you can coordinate these debugging tests with kimsland and kimsland's instructions. Consider
- Run Windows Update then copy/paste the list of High Priority Updates it lists into your post (or attachment to your post if it's long) so can see exactly what updates it's attempting
- Download Belarc Advisor. Run it to get a system profile and copy the profile into notepad and attach to a post (or at minimum copy the sections on installed Security Updates and Hotfixes from the Belarc profile and attach it to your next post)
Just fyi... i found that XP stores info on all updates in the registry (is where Belarc finds it to summarize) under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates. Belarc should provide a full formatted list of all the updates but just for visual comparison to check for registry corruption, the subkeys on my XP Pro SP3 installation under HKLM\....\Updates are:
.NETFramework
MSXML4SP2
SpNpInst
WGA
Windows
Windows Media Format 11 runtime
Windows Media Format 11 SDK
Windows Media Format SDK
Windows Media Player
Windows Media Player 10
Windows Media Player 11
Windows Media Player 6.4
Windows Media Player 9
Windows Presentation Foundation
Windows XP
SP0
SP1
SP10
SP2
SP3
KB936929
WIC
SP4
XML Paper Specification Shared Components Pack 1.0