NEWB: get username that is currently logged in to Windows workstation.

I am sorry but I am somewhat new to interfacing Windows through PHP. What I am trying to do is to get the username (or otherwise unique identifier) of the user that is currently logged into the local Windows workstation, and then assign the username to a variable. Can it be done? Originally what I considered doing was, in ASP, obtain the username and write it to a cookie. Then use PHP to parse the cookie to get the username. -Aaron