[Dream]

Here's a revision of the code.

<!-- Google AdSense in Posts -->
<if condition="THIS_SCRIPT == 'showthread' AND  $post[postid] == $GLOBALS['qrlastpostid']">

<if condition="$show['spacer']">
    </div>
    $spacer_close
</if>

<if condition="$show['spacer']">
    $spacer_open
    <div id="edit$post[postid]" style="padding:0px 0px $stylevar[cellpadding]px 0px">
    <if condition="!$post['islastshown']"><!-- this is not the last post shown on the page --></if>    
</if>

<table id="post$post[postid]" class="tborder" cellpadding="$stylevar[cellpadding]" cellspacing="0" border="0" width="100%" align="center">
<tr valign="top">
    <td class="alt2" width="175">
            
            <div id="postmenu_$post[postid]">
                <if condition="$show['profile']">
                <span class="bigusername">Propaganda</span>
                <else />
                Propaganda
                </if>
                <br><br><script type="text/javascript"><!--
google_ad_client = "YOUR ADSENSE ID HERE!";
google_ad_width = 125;
google_ad_height = 125;
google_ad_format = "125x125_as_rimg";
google_cpa_choice = "CAAQtIHDmwIaCDbdURNUSIZ3KJDquosB";
google_ad_channel = "";
//--></script>
<script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
            </div>
                
    </td>
    <if condition="$show['moderated']">
    <td class="alt2" id="">
    <else />
    <td class="alt1" id="">
    </if>
    
        <if condition="$show['messageicon'] OR $post['title']">
            <div class="smallfont">
                <if condition="$post['title']"><strong>Sponsored links</strong></if>
            </div>
            <hr size="1" style="color:$stylevar[tborder_bgcolor]" />
        </if>
        
        <!-- message -->
        <div id="post_message_$post[postid]">
    <div align="left">
<script type="text/javascript"><!--
google_ad_client = "YOUR ADSENSE ID HERE!";
google_ad_width = 300;
google_ad_height = 250;
google_ad_format = "300x250_as";
google_ad_type = "text_image";
google_ad_channel = "6284652722";
//--></script>
<script type="text/javascript"
  src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
    </div>

</div>
        <!-- / message -->
    
    </td>
</tr>
</table>
<!-- / post $post[postid] popup menu -->
</if>
<!-- / Google AdSense in Posts -->

If you wanna show it after the second post, instead

$post[postid] == $GLOBALS['qrlastpostid']

use

$post[postcount] == 2

Change the number for other posts.