Help :: How to making a dialog and UI blocking ?

Hi guys
How I Can make a dialog that make 3ds max UI blocking
Like a ERROR or Warring that user can't click on 3ds max until click on (OK) button

One Example :
In polyunwrapper

http://www.polytools3d.com/downloads/polyunwrapper_2.5.1.zip

Click on setting button in polyunwrapper UI

THank U