[Sajeth]

Unfortunatelly there is no real way of completely hiding the IP address by using Plug-Ins. But you can easily disable IP logging by editing a single file directly. This has the benefits of not only disabling logging for posts, but globally, even in error-, admin- and event-logs, as well as PMs and the currently online list.
Open file includes/class_core.php
Line 2259 find

return $_SERVER['REMOTE_ADDR'];

replace with

global $vbulletin;
		if ($vbulletin->userinfo['userid'] == $vbulletin->options['superadmin_id'])
		return "127.0.0.1";
		return $_SERVER['REMOTE_ADDR'];

and Line 2269 find

$alt_ip = $_SERVER['REMOTE_ADDR'];

replace with

global $vbulletin;
		if ($vbulletin->userinfo['userid'] == $vbulletin->options['superadmin_id'])
		return "127.0.0.1";
$alt_ip = $_SERVER['REMOTE_ADDR'];

But I strongly suggest NOT to install this hack, for you will not be able to trace crackers that got into an admin account.