styling a search form

hi folks, this question may seem stupid to you, but I’m really getting mad at it. I’m styling a search box which uses the <?php get_search_form(); ?> hook.
I’ve given a background image to the #searchsubmit instead of the button, everything else is fine, but I really don’t know how to get rid of the text “Search” over the image!!
Do you know how can I do it?
Thanks a lot
k