prevID="sistemazione1";

function Fade(ID)
{
if(prevID!="sistemazione"+ID){
document.getElementById('sistemazione'+ID).style.display="block";
fadeout(prevID,100);
fadein("sistemazione"+ID,0);
prevID="sistemazione"+ID;
}
}

function fadeout(obj,op){
 document.getElementById(obj).style.MozOpacity=op/100;
 document.getElementById(obj).style.opacity=op/100;
 document.getElementById(obj).style.filter="alpha(opacity="+op+")";
 op=op-5;
 if(op>=0){
 window.setTimeout("fadeout('"+obj+"', "+op+")",0);
 } else {
 document.getElementById(obj).style.display='none';
 }
}

function fadein(obj,op){
 document.getElementById(obj).style.MozOpacity=op/100;
 document.getElementById(obj).style.opacity=op/100;
 document.getElementById(obj).style.filter="alpha(opacity="+op+")";
 op+=5;
 if(op<=100){
 window.setTimeout("fadein('"+obj+"', "+op+")",0);
 }
}