Are you looking for something similar to this page? This uses iframe tag. Just click Submit without filling in the form to get an idea of how it works.

You need to create 2 files. As an example we'll call it chat.

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In your scripts directory copy sample.inc.php, rename it chat.inc.php and edit the following lines:

33. Change page_sample_gpc to page_chat_gpc
59. Change page_sample_run to page_chat_run
79. Change PAGE TITLE to Chat (or whatever page title you want)
86. After <<<BREADCRUMB press enter to drop to a new line and type Chat (line 87)
93. Change sample to chat (this is what your template will be called in the next stage)

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Next, go to your template directory, create a new template called chat.tpl and do something similar to this:
Code
{$tbopen}
<tr><td class="lefttdheader">
Chat
</td></tr>
<tr><td class="alt-1">
<table align="center" width="98%" cellpadding="6" cellspacing="0">
<tr><td class="alt-1" valign="top">

<iframe width="100%" frameborder="0" allowtransparency="true" align="top" height="400" src="/chat.php"></iframe>

</td></tr></table>
</td></tr>
{$tbclose}
You'll obviously have to change the src="/chat.php" to your own details.

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Once you have done that, you can edit the language file so that it will show who is using that page on Who's Online.

CP > Display Options > Languages > Language Editor > Choose Specific Language File: online.php > Go

Then add:
Key - chat
String - Viewing the Chat page