function popup(mylink, windowname, width, height) {
	if ( width == null) {
		width = 950;
	}
	
	if ( height == null) {
		height = 730;
	}
	
	if (! window.focus) {
		return true;
	}
    		
	var href;

	if (typeof(mylink) == 'string') {
		href=mylink;
	}
	else {
		href=mylink.href;
	}
	
	var screen_width = screen.width;
	var screen_height = screen.height;
	var pos_x = (screen_width/2)-(width/2);
	var pos_y = (screen_height/2)-(height/2);

	window.open(href, windowname, 'width=' + width + ',height=' + height + ',left=' + pos_x + ',top=' + pos_y + ',scrollbars=no,toolbar=no,location=no,status=no,resizable=yes');
	
	return false;
}