Actually, it is the right forum - an OS update. KB982670 is not an auto update for XP. It is an optional one that is not needed.
"Specifically, the .NET Framework 4 Client Profile is released as a recommended update that may be installed automatically on Windows Vista and Windows 7. The Client Profile is released as an optional update for Windows XP. In Windows XP, you must manually run WU and select the .NET Framework 4 Client Profile."