getting notification when workstation un-locked by the user

From: z. f. (zigi_at_info-scopeREMSPAM.co.il)
Date: 11/29/04 

Date: Mon, 29 Nov 2004 13:47:45 +0200

Hi,

i want to get a notification when a windows 2000/xp/2003 machine state is changed from Locked to unlocked (GUI) like msn-messenger gets this notification and changes the status from online to away and vise-versa.

is there some API to register to this event? or how is it done?

TIA, z.