Код:
<object id="my_flash_obj" data="SWF/index1024х768.swf" type="application/x-shockwave-flash" width= "900" height= "600">
<script language="javascript">
var clientWidth = document.documentElement.clientWidth ? document.documentElement.clientWidth : document.body.clientWidth;
var my = document.getElementById('my_flash_obj');
my.width = clientWidth;
</script>