A quick update on this. A friend told me I could find uninstall information in C:\Windows\$NtUninstallKB826939$ (for example), so I attempted that, same result.
On a whim, and with no other alternatives, I reinstalled XP Pro over the existing system. This restored nearly everything back to the way it was, though I'm having to install apps as needed for various little hangups that I experience.
Does anyone know why Windows Update would hose the computer so badly? Should I install the patches one at a time in the future? (I never had to worry with this stuff on Windows 2000.)
Thanks for any feedback.
Just finished perfecting my new Dell Latitude D600 running Windows XP Pro, and decided to be a good citizen by installing the Micro$oft critical security updates from WindowsUpdate.microsoft.com. There were some 23 packages waiting (critical only, mind you), and I installed them all. After they installed and I rebooted, all hell broke loose.
I was on my office network, but on reboot XP wouldn't detect the wired network that was connected, nor the wireless network that worked fine just moments before.
I first noticed that the Windows taskbar's appearance changed back to the Windows 2000 style. My network connections are GONE; when I try to create some new ones, the message "Windows networking is not installed or is installed incorrectly." The Windows key on the keyboard doesn't display the Start Menu--though I can still use Windows+E to open Explorer, Windows+R to run. I can't drag and drop, copy-cut-or-paste. Windows+F doesn't display the search window. The Windows taskbar doesn't display open applications. After fiddling with all this for a while, now the My Documents, My Computer, and Network Places icons are no longer on the desktop, and the taskbar is permanently shrunk against the bottom of my screen; I can't even stretch it back up like it should. I checked to make sure I added my username into the local Administrators group; when I open the Administrator's group, the message appears: "The RPC Server is unavailable."
I inserted a blank CD-R to back up some recently-modified files and received this message: "The Windows Installer Service could not be accessed. This can occur if yo uare running Windows in safe mode, or if the Windows Installer is not correctly installed. Contact your support personnel for assistance." It did allow me to burn a CD, though.
Fortunately, I can still view installed programs in the control panel. Here are the hotfixes listed; note that I can't uninstall any of them:
Outlook Express Update Q330994 "There was an error trying to uninstall this patch."
Windows Media Player hotfix [See Q828026 for more information] - Goes through the motions of uninstall, even reboot, but still appears in the programs list after reboot
Windows XP Hotfix - KB817611
Windows XP Hotfix - KB823182
Windows XP Hotfix - KB824105
Windows XP Hotfix - KB824141
Windows XP Hotfix - KB825119
Windows XP Hotfix - KB826939
Windows XP Hotfix - KB826959
Windows XP Hotfix - KB828028
Windows XP Hotfix - KB828035
Windows XP Hotfix (SP2) Q819696
Any ideas? I *am* the support personnel in this case, and feel like a sitting duck. Any help is appreciated!

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