title: How to get the last windows active time by windows api
body: <p>In general, the Screensaver will run when we do nothing for a period of time.<br/>
  Now i wanna know how to get the unactive time.<br/>
  In another word,i want to make a program which would run a function if we do nothing for a period of time.<br/>
  Now i can use mouse or keyboard hook to solve the problem.<br/>
  But you know,it needs administrator permissions. In another word,if in win vista or win 7,it is nauseating because of the UAC.<br/>
  I need an API such to get last windows active time.</p>