This picture shows the "New Posts" link in question:

[ATTACH]17938[/ATTACH]

Exclude forums
Edit this template:

Admin CP -> Styles & Templates -> Style Manager -> « » -> Navigation / Breadcrumb Templates -> navbar

Find this code and add the red code (two instances, scroll right):

Code:
		<if condition="$show['popups']">		
			<if condition="$show['searchbuttons']">
				<if condition="$show['member']">
				<td class="vbmenu_control"><a href="search.php?$session[sessionurl]do=getnew[color=red]&exclude=[color=blue]X,Y,Z[/color][/color]" accesskey="2">$vbphrase[new_posts_nav]</a></td>
				<else />
				<td class="vbmenu_control"><a href="search.php?$session[sessionurl]do=getdaily" accesskey="2">$vbphrase[todays_posts]</a></td>
				</if>
				<td id="navbar_search" class="vbmenu_control"><a href="search.php$session[sessionurl_q]" accesskey="4" rel="nofollow">$vbphrase[search]</a> <script type="text/javascript"> vbmenu_register("navbar_search"); </script></td>
			</if>
			<if condition="$bbuserinfo['userid']">
				<td id="usercptools" class="vbmenu_control"><a href="$show[nojs_link]#usercptools">$vbphrase[quick_links]</a> <script type="text/javascript"> vbmenu_register("usercptools"); </script></td>		
			</if>
		<else />		
			<if condition="$show['searchbuttons']">
				<td class="vbmenu_control"><a href="search.php$session[sessionurl_q]" accesskey="4">$vbphrase[search]</a></td>
				<if condition="$show['member']">
				<td class="vbmenu_control"><a href="search.php?$session[sessionurl]do=getnew[color=red]&exclude=[color=blue]X,Y,Z[/color][/color]" accesskey="2">$vbphrase[new_posts_nav]</a></td>
				<else />
				<td class="vbmenu_control"><a href="search.php?$session[sessionurl]do=getdaily" accesskey="2">$vbphrase[todays_posts]</a></td>
				</if>
			</if>
			<td class="vbmenu_control"><a href="forumdisplay.php?$session[sessionurl]do=markread" rel="nofollow">$vbphrase[mark_forums_read]</a></td>
			<if condition="$bbuserinfo['userid']">			
				<td class="vbmenu_control"><a href="#" onclick="window.open('misc.php?$session[sessionurl]do=buddylist&amp;focus=1','buddylist','statusbar=no,menubar=no,toolbar=no,scrollbars=yes,resizable=yes,width=250,height=300'); return false;">$vbphrase[open_buddy_list]</a></td>			
			</if>			
		</if>
Where X,Y,Z is a comma list of excluded forumids.

Include forums (thereby excluding others)
Edit this template:

Admin CP -> Styles & Templates -> Style Manager -> « » -> Navigation / Breadcrumb Templates -> navbar

Find this code and add the red code (two instances, scroll right):

Code:
		<if condition="$show['popups']">		
			<if condition="$show['searchbuttons']">
				<if condition="$show['member']">
				<td class="vbmenu_control"><a href="search.php?$session[sessionurl]do=getnew[color=red]&include=[color=blue]X,Y,Z[/color][/color]" accesskey="2">$vbphrase[new_posts_nav]</a></td>
				<else />
				<td class="vbmenu_control"><a href="search.php?$session[sessionurl]do=getdaily" accesskey="2">$vbphrase[todays_posts]</a></td>
				</if>
				<td id="navbar_search" class="vbmenu_control"><a href="search.php$session[sessionurl_q]" accesskey="4" rel="nofollow">$vbphrase[search]</a> <script type="text/javascript"> vbmenu_register("navbar_search"); </script></td>
			</if>
			<if condition="$bbuserinfo['userid']">
				<td id="usercptools" class="vbmenu_control"><a href="$show[nojs_link]#usercptools">$vbphrase[quick_links]</a> <script type="text/javascript"> vbmenu_register("usercptools"); </script></td>		
			</if>
		<else />		
			<if condition="$show['searchbuttons']">
				<td class="vbmenu_control"><a href="search.php$session[sessionurl_q]" accesskey="4">$vbphrase[search]</a></td>
				<if condition="$show['member']">
				<td class="vbmenu_control"><a href="search.php?$session[sessionurl]do=getnew[color=red]&include=[color=blue]X,Y,Z[/color][/color]" accesskey="2">$vbphrase[new_posts_nav]</a></td>
				<else />
				<td class="vbmenu_control"><a href="search.php?$session[sessionurl]do=getdaily" accesskey="2">$vbphrase[todays_posts]</a></td>
				</if>
			</if>
			<td class="vbmenu_control"><a href="forumdisplay.php?$session[sessionurl]do=markread" rel="nofollow">$vbphrase[mark_forums_read]</a></td>
			<if condition="$bbuserinfo['userid']">			
				<td class="vbmenu_control"><a href="#" onclick="window.open('misc.php?$session[sessionurl]do=buddylist&amp;focus=1','buddylist','statusbar=no,menubar=no,toolbar=no,scrollbars=yes,resizable=yes,width=250,height=300'); return false;">$vbphrase[open_buddy_list]</a></td>			
			</if>			
		</if>
Where X,Y,Z is a comma list of included forumids.