I tested a little. Lets say your frameset looks like this.
CODE
<frameset cols="30%,70%">
<frame name="menu" src="menu.html">
<frame name="content" src="content.html">
</frameset>
Put a script block in HEAD of you frameset document with this.
CODE
function loadIt()
{
var whatSite = window.location.search;
whatSite = whatSite.replace("?site=", "");
if (whatSite == 'htmlhelp')
window.frames['content'].location = 'http://htmlhelp.com';
}
window.onload = loadIt;
Let's say your URL is
http://example.com . If you access it with this URL
http://example.com?site=htmlhelp then htmlhelp.com should load in the content frame. That is, you add a query string to the end of your URL in the format ?name=value.
You'd need to change the so it uses your name of the frame where the page should load and uses what you choose as querystring. And if you want to be able to load different sites this way you need to build on the if else a bit.