[Trip]

There's probably a couple of different ways you could do this...
Paste this into your additional CSS box.

.adCopy {
    text-align:center;
    }

Then try using this in place of your code. Note I omitted that closing script statement.

 <div class="adCopy">
    <a href="http://gtmdecals.com" target="_blank"><img src=
    "http://motorbicycling.com/images/misc/decals.gif" /></a>

    <div class="smallfont adCopy">
      <a href="http://gtmdecals.com" target="_blank">Motorized Bicycle Decals!</a>
    </div>
  </div>
<br />
<br />

I'm no pro, I was just cruising through and seen your post