If you have Windows XP and are receiving the Windows Update Error 0x80070420, please follow the steps below to solve it.
First, Check to see if you have Windows Installer 3.1 installed on your computer. To do this follow these steps:

1) Click on Start, Control Panel
2) Double-click on Add/Remove Programs
3) Search your Program List for the program
Windows Installer 3.1

4) If you find it there, click on Remove to uninstall it. Then reboot your computer. If it is not there proceed to step 5.


5) Click on the following link to Microsoft's Download Center to download Windows Installer 3.1

http://www.microsoft.com/downloads/d...displaylang=en

6) Install Windows Installer 3.1 and reboot your computer

7) Go to Windows Update and try to download the updates again.

Note: sometimes you may also receive this error if Windows XP has not been activated. To read about How to Activate Windows XP, click on the following support article from Microsoft.