[JimmyN]

Change the three to what you want, its the postcount. There is many others in the forum, do a search
https://vborg.vbsupport.ru/showthread.php?t=96249 )this is after first post

<if condition="$post[postcount] == 3">

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<div style="padding:0px 0px $stylevar[cellpadding]px 0px">

<table class="tborder" cellpadding="$stylevar[cellpadding]" cellspacing="$stylevar[cellspacing]" border="0" width="100%" align="center">
<tr>
    <td class="thead" align="left">Sponsored Links</td>
</tr>
<tr>
    <td class="alt1" align="center">
        <center>Ad Sense Code Here</center>
</if>
    </td>
</tr>
</table>

</div>
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</if>