function openvenster(url, width, height, parameters) {
x=1;
y=1;
if (width == "" || width<=0) {
 width=300;
}
if (height == "" || height<=0) {
 height=350;
}
if (parameters == "") {
 parameters = "resizable=0,status=0,toolbar=0,scrollbars=0";
}
if(window.screen){
 per_ancho=(width/screen.width)*100;
 per_alto=(height/width)*100;
 win_ancho=(screen.width*per_ancho)/100;
 win_alto=(win_ancho*per_alto)/100;
 x=(screen.width-win_ancho)/2;
 y=(screen.height-win_alto)/2;
 y=y-40;
 if (y<0) {
  y=0;
  }
 }
w=window.open(url,"venstertje","width="+width+",height="+height+",left="+x+",top="+y+","+parameters);
if (window.screen) {
 w.focus();
 }
}



function belbios() {
 openvenster("belbios.html", 790, 406);
}