Insert the Windows Vista installation disc in the disc drive, and then restart the computer.
When you are prompted to restart from the disc, press any key.
When you are prompted, configure the Language to install, Time and currency format, and Keyboard or input method options that you want, and then click Next.
On the Install Windows page, click Repair your computer.
On the “System Recovery Options” page, click the version of the Windows Vista operating system that you want to repair, and then click Next.
On the System Recovery Options page, click Command Prompt.
Type cd C:\windows\winsxs, and then press ENTER.
Type ren pending.xml pending.old, and then press ENTER.
In Registry Editor, locate and then delete the following registry subkey:
HLKM\Offline Components\AdvancedInstallersNeedResolving
HKLM\Offline Components\PendingXmlIdentifier
HKLM\Offline Components\NextQueueEntryIndex
At the command prompt, type exit to exit Registry Editor. Press ENTER. Click Restart.
Reference: http://social.answers.microsoft.com/Forums/en-US/vistawu/thread/13dec2a0-2694-4b11-9b0c-9b8fbe6162ee