Ok I would like to display in a webpage if a user is connected on IRC. For example, a page called online.php will say if user is currently connected to the specified IRC server at the time.

Is this possible?

Mirc can do that only if every user you want to see have your mirc script which will tell the php if he's online. If you want to see if some user is on server without him having your script you have to user php code to do that, not mirc scripting.