function abrir_ventana(url, nombre, width, height, posicionamiento, x, y, scrolls){
	if(posicionamiento=="centrado"){
		x = (screen.width - width)/2;
		y = (screen.height - height)/2;
	}
	open(url, nombre, "width="+width+", height="+height+", screenLeft="+x+", screenTop="+y+", scrollbars="+scrolls);
}