filling out HTML forms

So, we are trying to design an account management page that allows users to manage all of their computer accounts in one place. We want to allow them to change their passwords for all of their accounts in one place, unfortunately, we don't have access to one of the machines to change their password. This machine has a web form available that allows users to change their passwords online, and we were hoping to somehow use the information that the users entered on our form to fill out the other form. Is something like this possible? It seems like I've heard of something like this before. Any direction at all on using PHP as a solution to this problem would be greatly appreciated. Thanks Amanda