I am not a coder and i was just changing the sizes as i noticed a little clickable dot.
Heres the code i am useing and it works for me

but as i said i am no coder so it might be wrong.
The just done the edit in the template mobnpc_shout i just changed the width and height a bit and had a play about to see what looked good.
Code:
<div class="cms_widget"><div class="block"><div class="cms_widget_header"><h3>ShoutBox</h3></div><div class="cms_widget_content"><!-- GCBOS --><div class="forumrowdata"><p class="subforumdescription" id="gcbos_notice"></p></div></div><ol id="c_gcbos" class="childforum"><li id="gcbos3" class="forumbit_post L2"><div class="forumrow table"><div id="gcbos_console" style="height: 130px; overflow: auto;width:100%">Loading...</div><vb:if condition="$show['member']"><input type="text" id="gcbos_input" style="width: 90%; height: 19px; margin: 1px;float:left;" autocomplete="off" /><button type="button" onclick="gcbos.sendInput();" style="width: 9%; height: 22px; margin: 0px; float: right;">Submit!</button><vb:else /><center>You Need to <a href="register.php">Register</a> to be able Shout</center></vb:if><script type="text/javascript">
gcbos = new gcbos_engine();
YAHOO.util.Event.onDOMReady(gcbos.init, gcbos, gcbos);
</script><!-- /GCBOS --></div></div></div>