Drupal 6, Webform submit query

Hi,
Here is a snippet of a webform i created through Webform Module. Drupal 6.
All i want is my custom code to be executed on submit. But no
documentation is precise.

<form action="/RWPS/?q=node/4"  accept-charset="UTF-8" method="post"
id="webform-client-form-4" class="webform-client-form"
enctype="multipart/form-data">
<div><div class="webform-component webform-component-textfield"
id="webform-component-md5"><div class="form-item"
id="edit-submitted-md5-wrapper">
 <label for="edit-submitted-md5">MD5: </label>
 <input type="text" maxlength="128" name="submitted[md5]"
id="edit-submitted-md5" size="32" value="" class="form-text" />
</div>
</div><div class="webform-component webform-component-textfield"
id="webform-component-sha256"><div class="form-item"
id="edit-submitted-sha256-wrapper">
 <label for="edit-submitted-sha256">SHA256: </label>

 <input type="text" maxlength="64" name="submitted[sha256]"
id="edit-submitted-sha256" size="64" value="" class="form-text" />
</div>
</div><input type="hidden" name="details[sid]" id="edit-details-sid"
value=""  />
<input type="hidden" name="details[page_num]"
id="edit-details-page-num" value="1"  />
<input type="hidden" name="details[page_count]"
id="edit-details-page-count" value="1"  />
<input type="hidden" name="details[finished]"
id="edit-details-finished" value="0"  />
<input type="hidden" name="form_build_id"
id="form-96640775ae006eafa3df3b980bdd2ead"
value="form-96640775ae006eafa3df3b980bdd2ead"  />
<input type="hidden" name="form_token"
id="edit-webform-client-form-4-form-token"
value="c2c0540261fb185ef87e38acd8cb2b1c"  />
<input type="hidden" name="form_id" id="edit-webform-client-form-4"
value="webform_client_form_4"  />
<div id="edit-actions" class="form-actions form-wrapper"><input
type="submit" name="op" id="edit-submit" value="Submit"
class="form-submit" />
</div>
</div></form>

form Id is : webform_client_form_4

Is there a way to write my own submit code , can anyone give me a precise
method that works.

I want to display a message when form submits to test that hook is called or
not ? I tried webform_submit()

in my case i wrote webform_webform_client_form_4_submit() hooks, does not
work.

-- 
Thanks and regards,
Rohit Sharma