function showPopup()
{
	var width = 500;
	var height = 600;
	var x,y;
	
	var pop_up = document.getElementById('popup');
	
	pop_up.style.display = "block";
	
	if (self.innerHeight) // all except Explorer
	{
		x = self.innerWidth;
		y = self.innerHeight;
	}
	else if (document.documentElement && document.documentElement.clientHeight) // Explorer 6 Strict Mode
	{
		x = document.documentElement.clientWidth;
		y = document.documentElement.clientHeight;
	}
	else if (document.body) // other Explorers
	{
		x = document.body.clientWidth;
		y = document.body.clientHeight;
	}
	
	midX = (x / 2) - (width / 2);
	midY = (y / 2) - (height / 2);
	
	pop_up.style.left = midX+"px";
	pop_up.style.top = midY+"px";
}

function hidePopup()
{
	var pop_up = document.getElementById('popup');
	
	pop_up.style.display = "none";
}