When you try to install Vista SP1 from windows update you may receive the error code 80073712.This is the most common problem for many users.I hope this solution will work for you.
The issue is that the WUA 3.0 (7.0.6000.374) upgrade is corrupted,essentially the system reports the WUA to be 7.0.6000.374 but the files on the disk are still from the old version (you can check some of the DLLs like wups.dll, wuaueng.dll etc… in the windows\system32) … and you cannot install the WUA 3.0 even manually.
delete the following file
Since Windows security will not allow you to do this, here under the procedure to take ownership of the file
run a command prompt with “Run as Administrator”.
Type in the following commands
takeown /f C:\Windows\winsxs\pending.xml
cacls C:\Windows\winsxs\pending.xml /G <YourUsername>:F
then delete the file and Reboot the machine
Reinstall the Windows Update Agent
Windows, x86-based systems download from here
Windows, x64-based systems download from here
save to the desktop, and run from an elevated command prompt, adding /wuforce to the end of the command