var last_expanded = '';

function showHide(id)
{
var obj = document.getElementById(id);

var status = obj.className;

if (status == 'hide') {

if (last_expanded != '') {
var last_obj = document.getElementById(last_expanded);
last_obj.className = 'hide';
}

obj.className = 'show';

last_expanded = id;
} else {
obj.className = 'hide';
}
} 
//http://www.interspire.com/content/articles/10/1/Building-An-Expanding-DHTML-Menu-With-CSS-and-JavaScript