Pass javascript variable to flashvars

Hi,

I can currently pass and variable with javascript from a button.  But I cannot retrieve and use this value in flashvars so I can put variables on the end of the url.  This is slightly different in that I'm also use the value with ajax to pass the value to a database insert, to update my database record, in response to a users action.  When I use document.write there's nothing written, I'm wondering whether I can actually use that value after it's been sent or whether I'm going about it completely the wrong way....  Thanks

########################################################################

<script type="text/javascript">

'get value from onclick button then do ajax

function doSomething(str)
{

// get HttpRequest object and assign it to xmlhttp
xmlhttp=GetXmlHttpObject();
// Check browser support
if (xmlhttp==null)
  {
  alert ("Browser does not support HTTP Request");
  return;
  }
// The URL where your database processing will be done
var url="myurldatabaseupdate.php";

// Add your argument to this URL as a query string

url=url+"?ID="+str;

url=url+"&sid="+Math.random();

xmlhttp.onreadystatechange=stateChanged;

// Send request to the server
xmlhttp.open("GET",url,true);
xmlhttp.send(null);

}

function stateChanged()
{

// readyState 4 means the request to the server is complete.
if (xmlhttp.readyState==4)
{

// xmlhttp.responseText contains any text output on the page where you processed your database request.

document.getElementById("url").innerHTML=xmlhttp.responseText;

}
}

// Function to get HttpRequest object
function GetXmlHttpObject()
{
if (window.XMLHttpRequest)
  {
  // for IE7+, Firefox, Chrome, Opera and Safari
  return new XMLHttpRequest();
  }
if (window.ActiveXObject)
  {
  // for IE6 and IE5
  return new ActiveXObject("Microsoft.XMLHTTP");
  }
return null;
}

</script>

###################################################################################

<no script>

/click to play buttons with track id,

<button type="button"  onclick="doSomething('717');" return false;>track1 play</button>
<button type="button"  onclick="doSomething('892');" return false;>track2 play</button>
<button type="button"  onclick="doSomething('983');" return false;>track3 play</button>

<object id='mySwf' classid='clsid:D27CDB6E-AE6D-11cf-96B8-444553540000' codebase='http://fpdownload.macromedia.com/get/flashplayer/current/swflash.cab' height="380" width="390">
        <param name='src' value='flashplayer.swf'/>
        <param name='flashVars' value='dataPage=theurl.com?id='+url+''/>
<embed name='mySwf' src='flashplayer.swf' pluginspage='http://www.adobe.com/go/getflashplayer' height="380" width="390" flashVars='dataPage=theurl.com?id='+url+''/>

</no script>