script to highlight all options in multiple select box

I'm guessing this is probably a job for JavaScript.

I have a form which allows people to enter email addresses one at a time into an input box with a button that places these values into a multiple select box on the same form (I do it this way because I can't trust end users to put all addresses in at once and leave it up to them to comma separate them).

What I need is a way to auto-highlight all the entries made into the select box when the form is submitted so that I can get all the entered values when I submit the form. Any ideas?

Thanks!!!!!!!!!!!

Can you post the code you've got? I'll help, I just can't be arsed to
make up all the html you've already done...