How to center my navabar

[goshalim]

Please any one ?? do you need the code as well of this navbar ??

<!-- Top Menu -->
<div id="MainMenu">
	<div id="tab">
		<ul>
			<li class="item_active">
<li "text-align: center">
<a href="$vboptions[homeurl]"><span>Home</span></a></li>
<li><a href="index.php"><span>Forum</span></a></li>
<if condition="$show['member']">
<li><a href="usercp.php$session[sessionurl_q]"><span>User CP</span></a></li></if>
<li><a href="memberlist.php$session[sessionurl_q]"><span>Λίστα Μελών</span></a></li>
<li><a href="calendar.php$session[sessionurl_q]"><span>Ημερολόγιο</span></a></li>
<li><a href="search.php?$session[sessionurl]do=getnew" accesskey="2"><span>Μυνήματα</span></a></li>
<li id="navbar_search"><a href="search.php$session[sessionurl_q]" accesskey="4" rel="nofollow"><span>Search</span></a><script type="text/javascript"> vbmenu_register("navbar_search" ,1); </script></li>
			<if condition="$show['registerbutton']">
			<li><a href="register.php$session[sessionurl_q]" rel="nofollow"><span>Register FREE!</span></a></li>
			<else />
<li id="usercptools"><a href="$show[nojs_link]#usercptools"><span>Quick Links</span></a><script type="text/javascript"> vbmenu_register("usercptools" ,1); </script></li></if>
<if condition="$show['member']">
<li class="vbmenu_control"><a href="login.php?$session[sessionurl]do=logout&amp;logouthash=$bbuserinfo[logouthash]" onclick="return log_out('$vbphrase[sure_you_want_to_log_out]')"><span>Έξοδος</span></a></li></if></li>
<li><a href="private.php$session[sessionurl_q]"><span>Προσωπικά Μηνύματα</span></a></li>
</div>
</ul>
</div>
	</div>
</div>