var impwin= null;
function OpenImpressum(){
var winl = (screen.width-600)/2;
var wint = (screen.height-500)/2;
var settings ='height=500,';
settings +='width=600,';
settings +='top='+wint+',';
settings +='left='+winl+',';
settings +='scrollbars=no,';
settings +='resizable=no';
impwin=window.open('impressum.html','impressum',settings);
}