function ajax_post( arquivo, parametro, nome_funcao )
{
	var xmlHttp;
	
	try
	{	// Firefox, Opera 8.0+, Safari
		xmlHttp = new XMLHttpRequest();
	}
	catch (e)
	{	// Internet Explorer
		try
		{
			xmlHttp = new ActiveXObject( "Msxml2.XMLHTTP" );
		}
		catch (e)
		{
			try
			{
				xmlHttp = new ActiveXObject( "Microsoft.XMLHTTP" );
			}
			catch (e)
			{
				alert( "Seu navegador não suporta AJAX" );
				return false;
			}
		}
	}

	xmlHttp.onreadystatechange = function()
	{
		if ( xmlHttp.readyState == 4 )
		{
			if ( nome_funcao )
			{
				eval( nome_funcao + "( xmlHttp.responseText )" );
			}
		}
	}

	var url = arquivo;
	xmlHttp.open( "POST", url, true );
	xmlHttp.setRequestHeader( "Content-Type", "application/x-www-form-urlencoded" );
	xmlHttp.send( parametro );
}