The following software-packages must be installed: Windows Installer 3.1, Windows Genuine Advantage-Testingtool and Update for Windows Xp (K898461). When you have installed these packages, so you go to the Windows-Update-Site and wait for the Windows-Update-Startsite.
Now you must copy this line

javascript:void(window.g_sDisableWGACheck='all')

and fill it in the address-panel and press Enter. The Windows-Update-Startsite will be reloaded and you have to press the custom-button to start the Windows-Update. The "normal Windows-Update" will be start.