Get Username From Windows Login

Dear all I'm using IIS Server 4.0, what i want to do is to prevent user to provide another login before they can reach my Intranet, so i had setted the php to grep the username from the windows, but here is the problem, the username that greped out was "IUSER_MICROSOFT", is there anyway that make the IIS to detect the username see if it is a valid account, then pass that account to php instead of using "IUSER_MICROSFOT". I want to show the user account of the real logged in user, not "IUSER_MICROSOFT". -- Thx a lot! Jack nedcor4@nedcor.com.hk