One of these two should work :

1. You need to run the system file checker.
It has to be run from an elevated Command Prompt. Click Start > All Programs > Accessories and right-click Command Prompt, then ‘Run as Administrator’. Type sfc /scannow (note the space) and press Enter. This may take some time and you may have to put the Vista DVD in the drive. Try to download the updates again.

2. You need to stop the WU service, rename the SoftwareDistribution folder and restart the WU service.
Make sure you are logged on as an Administrator and go to Start > Control Panel > Administrative Tools. Double-click Services (Provide the Administrator password or confirmation if prompted to do so) and right-click the Windows Update service then click Stop.

Start, type %windir% in the Start Search box and then press Enter. Locate and rename the SoftwareDistribution folder. This will erase your history on the Windows Update Site, which isn’t hugely important.

Start > Control Panel > Administrative Tools. Double-click Services (Provide the Administrator password or confirmation if prompted to do so) and right-click the Windows Update service then click Start. Try to download the updates again.

There is a third possibility, system restore, but for most people this has been going on for so long that the restore points were overwritten long ago.