problems with ajax

[eluser]dumbo[/eluser]
Hi, I'm new to CI as well as javascripts & AJAX. I have a noobie question about how to pass in a variable from the view's javascript and how to access it in the controller.

View's [removed]

Code:

var httpObj;
function checkName(username)
{
  httpObj = GetHttpObject();
  if(httpObj == null)
      {
          alert ("Browser does not support HTTP Request");
          return;
      }
  var url = <?php echo base_url().'index.php/addaccount/username_check';?>;
  url=url+"?q=" + username;
  url=url+"&sid;="+Math.random();
  httpObj.onreadystatechange=callback_account;
  httpObj.open("GET",url,true);
  httpObj.send(null);
}

function callback_account()
{
if (httpObj.readyState==4 || httpObj.readyState=="complete")
{
   alert(httpObj.responseText);
}
}


function GetHttpObject()
{
    var xmlHttp=null;
    try
     {
     // Firefox, Opera 8.0+, Safari
     xmlHttp=new XMLHttpRequest();
     }
    catch (e)
     {
     // Internet Explorer
     try
      {
      xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
      }
     catch (e)
      {
      xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
      }
     }
return xmlHttp;
}
[removed]

Controller's function:

Code:

function username_check()
   {
      echo($this->input->get('q'));
   }

So my question is can I actually pass in

Code:

"?q=" + username;

if I didn't activate query string in my config? If I can't, is there a way around this without using query strings?

My second question is how do I access that variable in controller after it's pass in?
Right now my username_check function returns blank.

Please let me know if there is anything unclear. Thanks.