I always have problems with updates to NetFramework, but its worse on Vista than other OSs. I would just hide it until other updates have been installed and then try it again. Make sure other programs are not running. Sometimes even the AV can cause problems, so that after it's down loaded, shut off the internet connection and disable the AV.
 have a dellE521 with home premium vista, 32. I've been trying to update  'Security Update for Microsoft. Net Framework 4 on XP,Server 2003,Vista, Windows 7. I keep on getting an error message 00000641. Can not find it under HELP. Is this something I need or can I just hide it?
windows updates