I am trying to figure out how to add a user from the web (w/ PHP or PERL): is it possible?

Of course its possible! You can do it with cgi in perl, shell or php with a simple html form.

I would not reccommend doing it since you can compromise the security of your system if you dont know what you are doing.

In PHP, you would:

make a form that sends the username and password... via POST, of course.

<?php

exec("adduser -u $HTTP_POST_VARS[user] -p $HTTP_POST_VARS[password]", $results);

?>

of course, it would be a good idea to use escapeshellcmd() (I forget the exact spelling, sorry - it's early and I haven't had any coffee), because a naughty user might semi-colon off your adduser command

Of course, the options for adduser vary per system... play with them and figure out what works!