getting height of a div tag default set to auto..

hi
i want my sidebar to be as long as my mainContent. so i want to find the height of my mainContent which is a div tag and has only width fixed to 600px. the height of this div can be as long as the text goes. so i want a javascript code that can find out this mainConten divs height. i tried using

document.getElementByID("mainContent").style.height

but it shows nothing... i heard somewhere that to get the height by javascript u must set the height by CSS. now i dont want my mainContent to have fixed height.. so what can i do now..

can someone give me a code which will tell me the current height of the mainContent without requiring the height to be set first??

thanks in Advance

 

here you go:

var h = document.getElementById('mydiv').offsetHeight;

 

thanks mate... u r a lifesaver...