[Alfa1]

Where do you want to display this?

Here is what I added to the template memberinfo_block_statistics to add a link to the posts in my wiki forum:

        <fieldset class="statistics_group">
        <legend>Wiki entries</legend>
        <ul class="list_no_decoration">
            <li><a  href="search.php?$session[sessionurl]do=finduser&amp;u=$userinfo[userid]&amp;starteronly=1&amp;forumchoice[0]=176"  rel="nofollow"><phrase 1="$prepared[username]">Find all wiki's  written by $prepared[username]</phrase></a></li>

As you see it doesn't have any way to display the number of posts made by the member, because there is no conditional for this. This code only shows the layout and the search for a members posts in a specified forum. If you want to use this, then replace 176 by the forumID of your forum, and edit the description accordingly.
To add a conditional, you would need to add a plugin. Review the template memberinfo_block_statistics to see what it should do.

Basically what you need is to create the conditional $prepared[posts_in_forum_x]
If you have that, you can just reuse the code thats already in the template memberinfo_block_statistics, but add that conditional.

I hope that helps somewhat. Sorry for providing the complete answer.

This should be a simple thing for a coder to prepare.