How do you set up a URLRewrite for a form?

Question

if I have a form <form action=script.php> with a parameter like <input name=keyword>

so my URL would be like www.domain.com/script.php?keyword=keyword1

how do I use URLRewrite in this case to change it to www.domain.com/script/keyword1/

had this been a regular link i can easily do it.. but what got me was how to do this out of a form action as the browser automatically sets it to www.domain.com/script.php?keyword=keyword1 before it even hits the server

thanks