Ok so I've been searching everywhere for a fix for this, it seems this is unfortunately quite the wide-spread problem. Unfortunately for me, it seems that simply re-registering a .dll fixed it for many users, but I have seen many that it has not fixed go unresolved.

Starters: running Vista x64 Ultimate, SP1. Avast! Home anti-virus. Have not been able to upload since April. Running Windows Update gives the error 80070424. I can update Windows Defender's files manually through the security center. I ran the livecare complete scan antivirus and it found nothing. I tried the whole registering .dll's and nothing worked. I cannot install IE 8 (tried with updates). I also cannot install SP2 (error 0x80070424).

Now, the precurser BEFORE people jump in. Registering the %SYSTEMROOT%\SYSTEM32\REGSVR32.EXE %SYSTEMROOT%\SYSTEM32\WUAUENG.DLL --goes successfully--, which seems to have worked for most people, but does nothing for me.

Another person seems to have had the same issue here:
Windows Update Error Code: 80070424 - Vista Setup and Install
yet, it trails off when people start complaining about the WUAUENG.DLL error 0x80070005, which IS NOT MY ISSUE. The WUAUENG.DLL reregisters fine, BITS seems to be running fine, but still, error 80070424.

BITS is enabled manually and running (have also tried automatic, did nothing). While registering a list of .dlls, one or two will have the following error:

Regsvr32 QMGR.DLL - The module "QMGR.DLL" was loaded but the entry-point DllRegisterServer was not found. Make sure that "QMGR.DLL" is a valid DLL or OCX file and then try again

As for the reregistering the .DLLs, this is where the funny business seems to be happening. I was told to register these DLLs:

regsvr32 wucltux.dll
regsvr32 wuaueng.dll
regsvr32 wups2.dll
regsvr32 wuapi.dll
regsvr32 wudriver.dll
regsvr32 wups.dll
regsvr32 wuwebv.dll

Yet regsvr32 wudriver.dll gives the same error: Module was loaded but the entry-point was not found.

I cannot seem to find a specific thread/area that deals directly with these DLLs and this problem, although others have mentioned this issue, they just go unresolved. I even tried downloading the DLLs and swapping them, but that was a no-go (kept the originals as _old, then swapped them back after it did nothing).
BITS restore tool says that it is not needed at this time.

Any ideas?

This error have many meaning and faces -read below exactly and check all
Windows could not search for new updates - Code 80070424

Probably you have problem with other service

Thanks Flavius, I just read your response elsewhere right after posting this thread.

I finally got it fixed! It was the Windows Module Installer service that was missing, which meant that my trustedinstaller.exe was missing from the services folder (although there are other versions stored elsewhere in the windows folder). Don't know why; some said Avast detects it as a false-positive and they delete it, but I don't remember that ever happening. I followed your post on adding the reg file, I tried to see if the Vista repair worked when booting from the DVD, but found nothing (the utility never seems to fix anything), so I found a copy of the trustedinstaller.exe from someone with Vista 64 SP1, and placed it in the windows/servicing folder (after logging into the hidden admin account and taking ownership of the folder), when I restarted it said "installing updates step 3 of 3" (?), then logged in as usual, checked windows update, and poof, it worked! 67 updates, over 600MB!

Granted, that's the short-winded version of a very long process, but thanks so much for your posting and your help. Glad someone finally helped us beyond the simple WUAUENG.DLL reregistering.