ho scaricato il seguente script:

#showimage{
position:absolute;
visibility:hidden;
border: 1px solid #999999;
}

#dragbar{
cursor: hand;
cursor: pointer;
background-color: #999999;
min-width: 50px;
}

#dragbar #closetext{
font-weight: bold;
margin-right: 1px;
color: white;
font-family: Verdana, Tahoma, Geneva, Arial, Helvetica, sans-serif;
font-size:11px;
}
</style>
<script type="text/javascript">

var ie=document.all
var ns6=document.getElementById&&!document.all

function ietruebody(){
return (document.compatMode!="BackCompat")? document.documentElement : document.body
}

function enlarge(which, e, position, imgwidth, imgheight){
if (ie||ns6){
crossobj=document.getElementById? document.getElementById("showimage") : document.all.showimage
if (position=="center"){
pgyoffset=ns6? parseInt(pageYOffset) : parseInt(ietruebody().scrollTop)
horzpos=ns6? pageXOffset+window.innerWidth/2-imgwidth/2 : ietruebody().scrollLeft+ietruebody().clientWidth/2-imgwidth/2
vertpos=ns6? pgyoffset+window.innerHeight/2-imgheight/2 : pgyoffset+ietruebody().clientHeight/2-imgheight/2
if (window.opera && window.innerHeight)
vertpos=pgyoffset+window.innerHeight/2-imgheight/2
vertpos=Math.max(pgyoffset, vertpos)
}
else{
var horzpos=ns6? pageXOffset+e.clientX : ietruebody().scrollLeft+event.clientX
var vertpos=ns6? pageYOffset+e.clientY : ietruebody().scrollTop+event.clientY
}
crossobj.style.left=horzpos+"px"
crossobj.style.top=vertpos+"px"

crossobj.innerHTML='<div align="right" id="dragbar"><span id="closetext" onClick="closepreview()" style="cursor: pointer; cursor:hand;">Chiudi</span> </div>[img]'+which+'[/img]'
crossobj.style.visibility="visible"
return false
}
else
return true
}

function closepreview(){
crossobj.style.visibility="hidden"
}

function drag_drop(e){
if (ie&&dragapproved){
crossobj.style.left=tempx+event.clientX-offsetx+"px"
crossobj.style.top=tempy+event.clientY-offsety+"px"
}
else if (ns6&&dragapproved){
crossobj.style.left=tempx+e.clientX-offsetx+"px"
crossobj.style.top=tempy+e.clientY-offsety+"px"
}
return false
}

function initializedrag(e){
if (ie&&event.srcElement.id=="dragbar"||ns6&&e.target .id=="dragbar"){
offsetx=ie? event.clientX : e.clientX
offsety=ie? event.clientY : e.clientY

tempx=parseInt(crossobj.style.left)
tempy=parseInt(crossobj.style.top)

dragapproved=true
document.onmousemove=drag_drop
}
}

document.onmousedown=initializedrag
document.onmouseup=new Function("dragapproved=false")

</script>


attualmente la pop-up si apre infondo a destra
vorrei invece che si aprisse al cento del browser
mo non riesco a capire dove effettuare le modifiche nel codice
Qualcuno mi può aiutare
Grazie