Who told you that? The heat produced by the ibook is dissipated through the back of the computer. I've even emailed apple asking this, they said that heat from the ibook is dissipated though the back vents. If it was designed that way it would be mighty inefficient due to the gaps between the EMI shield and the heat-sink and the shield and the keyboard.
And if worse comes to worse the fan will turn on, and I hardly believe that the heat that is "dissipated through the KB" will be hot enough to damage a LCD. To be precautionary though just crack the lcd open a little though.
Back to the original post ive found a program that might help you. Havent tested it out though, Google is your friend.
http://www.macupdate.com/info.php/id/10564
Edit:: If you do