[Adrian Schneider]

Try something like this:

<div align="center" class="fluidheader">
	<a href="index.php"><img src="http://www.5thgen.org/forum/images/misc/5thgenlogo.gif" border="0" alt="5thgen.org Camaro Forums" /></a>
</div>

.fluidheader {
	width: 100%;
	background: url('/forum/images/misc/5thgenlogogradient.gif') repeat-x;
}

I also noticed your repeating gradient doesn't exist... that is probably the reason! (check path)