var win = null;
function NewWindow(mypage,myname,w,h,scroll){
LeftPosition = (screen.width) ? (screen.width-w)/2 : 0;
TopPosition = (screen.height) ? (screen.height-h)/2 : 0;
settings =
'height='+h+',width='+w+',top='+TopPosition+',left='+LeftPosition+',scrollbars='+scroll+',resizable'
win = window.open(mypage,myname,settings)
if(win.window.focus){win.window.focus();}
}

//so muss ein link dann aussehen! nur noch die richtige groesse angeben!!
//<a href="deineseite.htm" onClick="NewWindow(this.href,'name','400','480','no');return false" target="_blank">blabla</a>