Very simple forms processing question

Hi I want to set up a mailing list on a site, and I want a very simple register/deregister facility. So a text field for the email address, then an [add] button and a [remove] button. Now, what I really want is for both [add] and [remove] to be 'submit' type HTML buttons for the same form, but at the destination script I don't know how to tell which button was pressed, and I've a feeling I should only have one submit button. I can do what I want JavaScript, but can I do it just with PHP? Any clues, or am I not being clear? Cheers J