how to know that windows is lgged in

hi i want that is it possible that when i logged into windows my 8051 gets to know that a user has logged in and desktop has appear
is there any way i can do it .. like sending some commands thru software on usb port or sumthing like tht
i want to drive some external device depending upon the appearing of desktop
please help

This might help you

http://www.experts-exchange.com/Programming/Languages/C_Sharp/Q_24621132.html

[Topic moved to Computer > Software Forum]

i basically need a external acknowledgement i want to give that acknowledgement to micro controller 8051

after you come to know that user logged in or something you can invoke a thread that acknowledge microcontroller.

Windows runs the programs in a user's "Startup" folder when they log in.
You could write, and run, a simple program that says "Hello" to the 8051
using the serial port, USB or whatever.