Thanks so much for your reply.
I want to develop a web app (like Web OS) where openoffice product can be installed into. I mean that can allow openoffice product to be installed and used like other applications.
I'm not sure what you mean by "install into". You may well be able to create documents programmatically via PHP and you may even be able to run 'macro'-type programs written in php, via the API - not sure about that. BUT, I can't see how PHP can be used to write and OS-type application that can run openoffice. There are ways to get php to open local files, but I really don't think this will work. Anybody else?
Thank you everybody for your responses. I appreciate it all.
What I meant to say is: I want to develop a PHP platform like joomla or openerp where php apps can run.
How and what do I need to know and how can I start.
I am just an intermediate php progammer.
If you want to develop a joomla / drupal / wordpress clone then good luck - not for the faint-hearted and if you're doing this on your own, you'll probably need a couple of years!
I'm not sure what you mean by letting php apps run - php apps run pretty much on their own on a webserver/dbserver. Are you looking at building some sort of portal or developing implementations of popular apps?