center edited header

First, Floridave, much help on everything so far

I have been playing with gallery2, and decided to try editting the theme.tpl and put my head/.jpg with a link back to my website. How do I center my image? here is the script I used.

<div id="gsHeader">
<img src="{g->url href="images/melikeylogo.jpg"}" width="50%" height="248" alt=""/>
</div>
{g->theme include="progressbar.tpl"}
{else}
<div id="gsHeader">
<a href="http://melikey.com/melikeytest"><img src="{g->url href="images/melikeylogo.jpg"}"
width="50%" height="248" alt=""/></a>
</div>