A technician at Microsoft suggested getting the software from here.
One of them, involving re-registering DLLs, was my fallback if the first suggestion didn't work.
Scott Dunn from Windows Secrets covered re-registering Windows Update DLLs last September in Stealth Windows update prevents XP repair.
In my case, this debugging information proved critical.
A Microsoft technician responded to my plea for help well within their 24 hour goal.
Time Required: It usually takes around 15 minutes to update a driver a Windows, even less time if the driver is self-installable or you get it via Windows Update (more on all of that below).
Follow the easy steps below to update drivers in Windows 10, Windows 8, Windows 7, Windows Vista, or Windows XP: Optional Walkthrough: If you'd like to follow the process below, but with more details and screenshots for each step, use my Step by Step Guide to Updating Drivers in Windows instead.
The "half" is a file called "Windows Update.log" which doesn't seem to be used any longer.
I checked four XP machines and in each case the file had almost no data and hadn't been updated in a long time.
If you've had problems with Windows Update after installing Windows XP SP3 leave a comment below.
I don't use Automatic Updates, but if you do, and find the yellow shield never goes away, you may be experiencing this problem.
Update: A reader named Joseph pointed out that this is from an older version of Windows Update.(July 27, 2008) But the other log file, "Windows Update.log" is a gold mine of information (this file has no spaces in the name).