var request = false;

try 
{
	request = new XMLHttpRequest();
}
catch (trymicrosoft) 
{
	try 
	{
		request = new ActiveXObject("Msxml2.XMLHTTP");  
	}
	catch (othermicrosoft) 
	{
		try 
		{
			request = new ActiveXObject("Microsoft.XMLHTTP");    
		}
		catch (failed) 
		{    
			request = false;    
		}
	}
}

if (!request)
	alert("Error initializing XMLHttpRequest!");