I’ve always thought you would need a hidden submit button in order to submit a form.  Well thats not true, for search boxes on certain blogs and forums, etc..  All they use is a form wrapped around the input box its really simple really example:

<form method='post' action='http://google.com'>
<input type='text' name='test' />
</form>

And that’s all to it. Have fun submitting!.