This is impossible >.>

[Koutaru]

Sure ^^; it's in my header and navbar templates. If it looks messy, forgive me
header

<if condition="$avatarurl && !$show['guest']"><img src="$avatarurl" border="0"><else /><img src="http://images.miyechi.com/avatar/noavatar.gif" border="0"></if></a>



 <!-- breadcrumb, login, pm info -->
	<if condition="$bbuserinfo['userid']">
		<td valign="top" nowrap="nowrap">
		<div class="smallfont">
			<span style="float:$stylevar[right]">
			<strong><phrase 1="$bbuserinfo[username]">$vbphrase[welcome_x]</phrase></strong><br>
			<if condition="$show['pmstats']"><phrase 1="$vbphrase[unread_x_nav_compiled]" 2="$vbphrase[total_x_nav_compiled]" 3="$session[sessionurl]">$vbphrase[private_messages_nav]</phrase></if><br>
[<a href="http://www.miyechi.com/login.php?$session[sessionurl]do=logout&amp;u=$bbuserinfo[userid]" onclick="return log_out()">$vbphrase[log_out]</a>]</span>
		</div>
		</td>
		
	<else />
		
		<td nowrap="nowrap" style="padding:0px">
			
		<!-- login form -->
		<form action="http://www.miyechi.com/login.php" method="post" onsubmit="md5hash(vb_login_password,vb_login_md5password)">
		<script type="text/javascript" src="clientscript/vbulletin_md5.js"></script>
		<table cellpadding="0" cellspacing="$stylevar[formspacer]" border="0">
		<tr>
			<td><input type="text" class="button" name="vb_login_username" id="navbar_username" size="10" accesskey="u" tabindex="1" value="$vbphrase[username]" onfocus="if (this.value == '$vbphrase[username]') this.value = '';" /></td>
			<td class="smallfont" colspan="2" nowrap="nowrap"><label for="cb_cookieuser_navbar"><input type="checkbox" name="cookieuser" value="1" tabindex="3" id="cb_cookieuser_navbar" accesskey="c" checked="checked" />$vbphrase[remember_me]</label></td>
		</tr>
		<tr>
			<td><input type="password" class="button" name="vb_login_password" value="$vbphrase[password]" size="10" accesskey="p" tabindex="2" onfocus="if (this.value == '$vbphrase[password]') this.value = '';" /></td>
			<td><input type="submit" class="button" value="$vbphrase[log_in]" tabindex="4" title="$vbphrase[enter_username_to_login_or_register]" accesskey="s" /></td>
		</tr>
		</table>
		<input type="hidden" name="s" value="$session[sessionhash]" />
		<input type="hidden" name="do" value="login" />
		<input type="hidden" name="forceredirect" value="1" />			
		<input type="hidden" name="vb_login_md5password" />
		</form>
		<!-- / login form -->
		</td>
	</if>	
<!-- / breadcrumb, login, pm info -->

You can see it in action here:
http://www.miyechi.com/forum.php

It's just trying to distinct between registered users and guests basically :/