(You emailed me: "You are right with that. I'm to use the URL from the querystring and set it as the source for one of the frames within a frameset.")
Ok, that's easy enough. The php page should look like this:
<?php
if (isset($GET['url']))
$url = urldecode($GET['url']);
else
$url = "defaultpage.php";
?>
.
.
.
<frameset>
<frame src="thispage.php">
<frame src="<?=$url?>">
</frameset>
Then, assuming that page is called index.php, if the user goes to "index.php?url=mypage123.php" then the second frame will contain mypage123.php. If no page is specified in the query string, then the frame will contain defaultpage.php.
Hope that helps!