var visible_div = null;

function show_hide( id )
{
	if ( visible_div )
		{ hide_div(visible_div); } 
	
	visible_div = document.getElementById(id);
	show_div( visible_div );
}  

function show_div( n ) 
	{ n.style.display = "block"; }

function hide_div( n )
	{ n.style.display = "none"; }

window.onload = function()
{
	visible_div = document.getElementById( 'c1' );
	show_div( visible_div );
	hide_div( document.getElementById( 'c2' ) );
}