//here you place the ids of every element you want.
var ids=new Array('a1','a8','a2','a3','a4','a5','a6','a7','a9','b1','b2');

function switchid(id){	
	hideallids();
	showdiv(id);
}

function hideallids(){
	//loop through the array and hide each element by id
	for (var i=0;i<ids.length;i++){
		hidediv(ids[i]);
	}		  
}

function hidediv(id) {
	//safe function to hide an element with a specified id
	if (document.getElementById) { // DOM3 = IE5, NS6
		document.getElementById(id).style.display = 'none';
	}
	else {
		if (document.layers) { // Netscape 4
			document.id.display = 'none';
		}
		else { // IE 4
			document.all.id.style.display = 'none';
		}
	}
}

function showdiv(id) {
	//safe function to show an element with a specified id
		  
	if (document.getElementById) { // DOM3 = IE5, NS6
		document.getElementById(id).style.display = 'block';
	}
	else {
		if (document.layers) { // Netscape 4
			document.id.display = 'block';
		}
		else { // IE 4
			document.all.id.style.display = 'block';
		}
	}
}

<!--
// PRELOADING IMAGES
if (document.images) {
 btn1_down=new Image(); btn1_down.src="btn1down.gif"; 
 btn1_up  =new Image(); btn1_up.src  ="btn1up.gif"; 

 btn2_down=new Image(); btn2_down.src="btn2down.gif"; 
 btn2_up  =new Image(); btn2_up.src  ="btn2up.gif"; 
}

// EVENT HANDLERS
function pressButton(btName) {
 if (document.images)
  eval('document.'+btName+'.src='+btName+'_down.src');
}

function releaseButton(btName) {
 if (document.images)
  eval('document.'+btName+'.src='+btName+'_up.src');
}
//-->