I agree with Steven, segments would be the most robust, quickest and simplest method.
JavaScript may be an option if you need more granularity or more custom options.
The text or entire block would be placed within HTML block page element. You can cut/paste the relevant source using the HTML button in the editor.
In that HTML block page element you can read the URL parameter and display the respective content.
The JavaScript will be similar to:
<script language="Javascript" src="/js/public/jquery-latest.min.js" type="text/javascript"></script>
<script src="/js/public/jQueryString-2.0.2-Min.js" type="text/javascript" ></script>
<script>
// to set cookies. Uses noConflict just in case
var $jQ = jQuery.noConflict();
var pState = $jQ.getQueryString({ ID: "State" });
switch(pState)
{
case 1:
execute code block 1
break;
case 2:
execute code block 2
break;
default:
code to be executed if n is different from case 1 and 2
}
</script>
Please keep in mind I did not fully test it while writing my reply.
Please have a developer to validate before posting to production.