Replace a string in content

Hi,

I am trying yo write my first plugin where it will look in the content of a post for the {charts 1.xml} and replace with a javascript snippet

<script type="text/javascript" src="swfobject.js"></script>

	<div id="flashcontent">
		<strong>You need to upgrade your Flash Player</strong>
	</div>
	<script type="text/javascript">
		// <![CDATA[
		var so = new SWFObject("tock.swf", "stock", "800", "400", "8", "#F9F9F9");
		so.addVariable("path", "");
		so.addVariable("settings_file", encodeURIComponent("1.xml"));
        so.addVariable("preloader_color", "#999999");
		so.write("flashcontent");
		// ]]>
	</script>

I know how to replace {chart} into what I need but I can’t think of the best way to replace {chart 1.xml} where I can put whatever file I want.

Thanks for any advice in advance