I'm trying to position 3 images that stay in the middle of the screen regardless of the resolution and without using a table to do it. I think it can be done via a style sheet, but how?

<div class="x">
<img alt="front_1.gif (3K)" src="Images/front_1.gif" height="54" width="700"><br>
<img alt="front_2.gif (10K)" src="Images/front_2.gif" height="63" width="700"><br>
<img alt="front_3.gif (13K)" src="Images/front_3.gif" height="61" width="700"><br>
</div>
These would be the images