Code: 
<if condition="$post['field5']">
<div style="border:1px solid #c9c9c9; background:#f6f6f6; padding:2px; margin-bottom:3px;">

Gamer Tag: <a href="http://live.xbox.com/member/$post[field5]">$post[field5]</a>

</div>
</if>
I would suggest:

Here is what you need:

Code: 
<if condition="$post['field5']">
<div style="gamertag">

Gamer Tag: <a href="http://live.xbox.com/member/$post[field5]">$post[field5]</a>

</div>
</if>
And in the additional CSS area of your style add:

Code: 
/* ***** styling for Gamer Tags ***** */
.gamertag { 
    background: #f6f6f6;
    border: 1px solid #c9c9c9;
    padding:2px;
    margin-bottom:3px;
    }
This way if you change styles, you can change it one area and not have to mess with templates. And you may want to validate this code. I'm rusty.

I did the first way but both work great.