[SVTBlackLight01]

Find this in the postbit template

	<td bgcolor="$post[backcolor]" width="175" valign="top" nowrap>
	<a name="post$post[postid]"></a>
	$post[firstnewinsert]
	<normalfont><b>$post[username]</b></normalfont><br>
	<smallfont>$post[usertitle]</smallfont><br>
	$post[avatar]<p>
	<smallfont>Registered: $post[joindate]<br>
	Location: $post[field2]<br>
	Posts: $post[posts]</smallfont></td>

Change the first line to include your image like this

 <td bgcolor="$post[backcolor]" background="/path/to/image.gif" width="175" valign="top" nowrap>

That should work.