Using PHP with windows logon

Hello all, I just have a quick question, I am not sure that it is even possible but im gonna take a whack anyways, basically what i want to know is, can you use your windows logon as set it as a variable in php?? eg I log onto a windows machine using brenton can i use a php script to set that as a variable, I have seen a similar type function before but i have no idea how it works, I know windows sets the variable %username% that as a network administrator i use in shortcuts to point to their home drive.. Hopefully i can do this :P Cheers in advance