While trying the install Service Pack 3 on the Windows XP Service Pack 2 Computer the following error messaged showed ‘c:\windows\system32\ntdll.dll’ is open or in use by another applications’ I was installing Service Pack 3 Through Windows Update. I downloaded and ran Process Explorer from SysInternals , This let me use the Find function for searching for process’ calling the ntdll.dll file. After looking at the list , and finding out the process with the type “HANDLE” I found the process using this DLL was infact internet explorer ( iexplorer.exe)! Since this update came from Windows Update there was obviously an issue. To resolve the issue , I downloaded  the standalone Network Version of SP3 and made sure Internet Explorer was closed before I reran setup Reran SP3 and the update worked fine!