If you get an access denied error while installing Windows XP sp3 then these steps might be of help to you.

First method:

Try downloading full install package from microsoft website and install it. It can be obtained by going to the link http://support.microsoft.com/kb/322389/.

Second method:

Restart the computer and disable any anti virus or anti spy ware program that you have on your computer. They can be disabled from the system tray icon. Just right click on the icon and click on close or disable. Then install the sp3 and then after finishing the install enable the anti virus again.

Third method:

This method is for advanced users only, because it involves steps to
modify the registry. Serious problems might occur if you modify the
registry incorrectly.

  1. Download and install the Subinacl.exe file. To do this visit the following Microsoft web site: http://www.microsoft.com/downloads/details.aspx?FamilyID=e8ba3e56-d8fe-4a91-93cf-ed6985e3927b&displaylang=en
  2. Start notepad.
  3. Copy and paste the following text into notepad.
    cd /d “%ProgramFiles%\Windows Resource Kits\Tools”
    subinacl /subkeyreg HKEY_LOCAL_MACHINE /grant=administrators=f /grant=system=f
    subinacl /subkeyreg HKEY_CURRENT_USER /grant=administrators=f /grant=system=f
    subinacl /subkeyreg HKEY_CLASSES_ROOT /grant=administrators=f /grant=system=f
    subinacl /subdirectories %SystemDrive% /grant=administrators=f /grant=system=f
    subinacl /subdirectories %windir%\*.* /grant=administrators=f /grant=system=f
    secedit /configure /cfg %windir%\repair\secsetup.inf /db secsetup.sdb /verbose
  4. Save this Notepad file as Reset.cmd.
  5. Double click the Reset.cmd file to run the script.

    Note: Script may take long time and should be run as administrator.

  6. Install Windows XP sp3.