[Javascript/HTML/PHP] Chat... / Updating page..

Hello i want to make it so there is a textbox on a page. When a user writes in the textbox and clicks the enter key on his/her keyboard the text the user entered will be added on the page... simulating a chat / mini-forum.

Basicly how do i edit the text of a page with JavaScript / HTML, if you can't then how about php..?

I have found some code:

Example:

Code:

---

<?php
$File = "YourFile.txt";
$Handle = fopen($File, 'w');
$Data = "Jane Doe\n";
fwrite($Handle, $Data);
$Data = "Bilbo Jones\n";
fwrite($Handle, $Data);
print "Data Written";
fclose($Handle);
?>

---

So i was thinking i can use this to edit my html page. Though now i need to place a frame of my other page that is being updated on my chat page. How do i place a frame showing my other page?...