Hi Joe and welcome to the forum
A well scripted first post....
A quick way to do this would be to open the index.main.php for that skin and find...

<div class="pageHeader">

	<div class="top_menu floatright">
		<?php
			// ------------------------- "Menu" CONTAINER EMBEDDED HERE --------------------------
			// Display container and contents:
			skin_container( NT_('Menu'), array(
					// The following params will be used as defaults for widgets included in this container:
					'block_start' => '',
					'block_end' => '',
					'block_display_title' => false,
					'list_start' => '',
					'list_end' => '',
					'item_start' => ' ',
					'item_end' => ' | ',
				) );
			// ----------------------------- END OF "Menu" CONTAINER -----------------------------
		?>
		<a href="<?php $Blog->disp( 'mediaidxurl', 'raw' ) ?>"><?php echo T_('Index') ?></a>
	</div>

Just after <div class="pageHeader"> I would place a new <div class="makealotofmoney">Banner code goes here</div>

In your style.css add div.makealotofmoney {text-align:center;margin:10px;} naturally use the css to style it to suit