Windows Update not working, error 0x8DDD0018

This can happen with Windows XP (Service Pack 3), but may not be ruled out for Vista and 7.

Windows Update error 0x8DDD0018, by which the Microsoft Update website now very helpfully explains that one or more of these services are not running:
* Automatic Updates
* Background Intelligent Transfer Service (BITS);
* Event Log

Even if all these services are running, and Windows Update refuses to run, then the culprit is the Windows Installer service not being active.

Run services.msc and then start Windows Installer. Refresh the Windows Update website. #worksforme