The link posted by Zen leads to a good read with good,
specific info.
Assuming you log on as Administrator, have already run malware scans (Anti-virus
plus Malwarebytes or Spybot Search&Destroy, for example), that come up clean, let's do some basic housekeeping:
1. Run Windows System File Checker (SFC):
Start> All Programs> Accessories. Right-click
Command Prompt click
Run As Administrator and type
sfc /scannow , then press
Enter. Let the utility run. Reboot.
2. Give this
Microsoft FixIt a try, which is supposed to, "Automatically diagnose and fix common problems with Windows Update. Automatically diagnose and fix common problems with Windows Update, keeping your PC more secure and reliable.":
http://support.microsoft.com/mats/windows_update/en-us
Reboot and try Updates again. If no luck, then:
3. Download and run Windows 7 Update Readiness Tool:
Windows6.1-KB947821. There are 32bit and 64bit versions. Choose the right one for your system. This Tool takes a good while to run and has NO progress indicator. Let it finish. Reboot and try your updates again.
Keep us posted.