The Windows Geniune Advantage tool is something that has drawn a lot of controversy in the past few months. Mainly because users accused it of being "spyware" since the tool would "check in" with Microsoft after Windows would start.
The WGA tool is parts of Microsofts plan to combat piracy of Windows. The WGA tool will display a message to users who have illegitimately obtained copies of Windows XP. In this update Microsoft has changed the installation procedure so that users will be able to better understand what exactly the WGA does.
This updated tool will be released through Windows Update soon.