Just a quick answer because I´m in a hurry.
Look at this code snippet (yes, I know, inline styling is bad

.
<div style="width:200px;height:200px;float:left">
<img style="display:block;height:100px;width:100px;margin:50px auto 0 auto" />
</div>
The container has defined width and height. Don´t forget to give it a float.
The image must get a d"isplay:block" before you can center it. Use the first value of the margin-attribute to define the distance from the top. This is the value you have to change according to the height of your image. The both "auto"-values will center your image horizontally.
Hope this will help, joshlfisher. And please: don´t use this code from the example, it is quick and dirty. Write CSS classes.