Refresh header and MIME types

Hi all. I would like to start making progress on an idea I have, in order to prepare several different modules for the project I mentioned in other mails before. One of them modules, is going to be a chat room. I would like to create my own but the problem I find (in my head as I haven’t worked on it yet) is the self-refreshing of the chat room. I don’t like using frames, and supposing the Site schema will be made using templates (or such), I would need to make PHP send a header telling the browser to update at certain intervals of time… let’s say 5 seconds. Is there a way to insert a header like this in the top of the header.php file, but tell it to refresh just the chatroom.php page which will be located below it??? Or it will work for the entire group of pages being displayed?? Also, I would need one of you to pin-point a site where I can learn about MIME types and how to use them in PHP… i.e. when sending mail. Thanks in advance, <mailto:webmaster@icaam.com.ar> Cesar Aracena CE / MCSE+I Neuquen, Argentina +54.299.6356688 +54.299.4466621