To fix this problem, try these steps:
1: Boot from Windows Vista DVD and on the Install Now screen, click Repair Your Computer.
2: Click Command Prompt.
3: Type cd C:\windows\winsxs and then press ENTER.
4: Type ren pending.xml pending.old and then press ENTER.
5: Type regedit and then press ENTER.
6: Go to HKEY_LOCAL_MACHINE. Now click on the File menu and then click Load Hive.
7: Locate the following folder:C:\windows\system32\config\components When you are prompted for a name, type Offline_Components.
8:In Registry Editor, locate and then delete the following registry subkey: HLKM\Offline Components\AdvancedInstallersNeedResolvingHKLM\Offline Components\PendingXmlIdentifier
9: Type exit and restart your computer.
NOTE: Even if u delete the PENDING.XML file, one can boot into the desktop.