创建支持多浏览器的XMLHttp

function getXMLRequester( )
{    
          var xmlhttp_request = false;   
          try
          {       
              if( window.ActiveXObject )
              {           
                  for( var i = 5; i; i-- )
                  {  
                       try
                        {                   
                                if( i == 2 )
                                {
                                      xmlhttp_request = new ActiveXObject( "Microsoft.XMLHTTP" );                       
                                   }
                                else
                                {    
                                      xmlhttp_request = new ActiveXObject( "Msxml2.XMLHTTP." + i + ".0" ); 
                                      xmlhttp_request.setRequestHeader("Content-Type","text/xml");xmlhttp_request.setRequestHeader("Content-                            Type","gb2312");                
                                    }
                                break;
                           }                   
                       catch(e)
                       {   
                                xmlhttp_request = false;              
                       }          
                  }       
             }
             else if( window.XMLHttpRequest )
             {         
                  xmlhttp_request = new XMLHttpRequest();           
                  if (xmlhttp_request.overrideMimeType) 
                  {   
                   xmlhttp_request.overrideMimeType('text/xml');            
                      }       
             }   
         }
        catch(e)
        {        
             xmlhttp_request = false;  
          }   
          return xmlhttp_request ;
      }