i did a search earlier but wasn't sure which one i used. i decided to lurk around my old templates and found the code in the posbit legacy. for those interested, here's the code.
Code:
<if condition="$post[postcount] == 1">
$spacer_open
<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>
(your adsense code goes here)
</tr>
</table>
</div>
$spacer_close
</if>
this mod will place a google add after the 1st post of a thread. it have it installed in v3.7.2 and it's working fine.