I'm at the end of my tether with this problem now, so any advice/help would be very much appreciated!
I am running Vista 32-bit SP2 and cannot successfully install KB2839229 no matter what I do. It fails with error code 80070020 every time. Initially it tells me that it has installed correctly, but on rebooting, configuring the update is unsuccessful. I have tried downloading the update directly and that fails in exactly the same way.
What I have tried so far:
Disabling all security software during the process
Running Microsoft's FixIt
Running Windows Repair (All in one)
I can't seem to do a clean reboot, msconfig hangs when I try to disable all but Microsoft services and WU will not run in Safe Mode with networking at all.