Code
<script type="text/javascript">
if (self.screen)
{
width = screen.width
height = screen.height
}
else if (self.java)
{
var jkit = java.awt.Toolkit.getDefaultToolkit();
var scrsize = jkit.getScreenSize();
width = scrsize.width;
height = scrsize.height;
}
if (width && height) var str = width + " на " + height;
else var str = "неизвестно";
document.writeln("ваш монитор: " + str)
</script>