www.yourwebsite.com?indexvariable=hello

Code:
<head>
<script src="AC_RunActiveContent.js" language="javascript"></script>
</head>
<body>
<script language="javascript">
var urladdress=window.location.href;
var myindex=urladdress.split("?indexvariable=")[1];

AC_FL_RunContent(
			'codebase', 'http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,0,0',
			'width', '200',
			'height', '910',
			'src', 'index',
			'quality', 'high',
			'pluginspage', 'http://www.macromedia.com/go/getflashplayer',
			'align', 'middle',
			'play', 'true',
			'loop', 'true',
			'scale', 'noscale',
			'wmode', 'transparent',
			'devicefont', 'false',
			'FlashVars', 'swfindex='+myindex,
			'id', 'index',
			'bgcolor', '#000000',
			'name', 'index',
			'menu', 'true',
			'allowFullScreen', 'false',
			'allowScriptAccess','sameDomain',
			'movie', 'index',
			'salign', ''
			);
</script>
</body>

Write this AS code on the main timeline(frame)

Code:
var variableFromHtml=swfindex;
trace(variableFromHtml);

// output: hello