Hi, open templates/header.tpl

Find these line:
<link href="{$baseurl}/templates/css/style.css" rel="stylesheet" type="text/css">
</head>
<body>


After <body> insert the following for the right side:

<table width="110" border="0" align="right" cellpadding="0" cellspacing="0" bgcolor="#FFFFFF">
<tr>
<td>
Favorite advertising code or zone goes here
</td>
</tr>
</table>

And then, for the left side, insert the following:
<table width="110" border="0" align="left" cellpadding="0" cellspacing="0" bgcolor="#FFFFFF">
<tr>
<td>
Favorite advertising code or zone goes here
</tr>
</td>


And right after the </td> above, is the following code already in the header:

<table width="780" border="0" align="center" cellpadding="0" cellspacing="0" bgcolor="#FFFFFF">
<tr>
<td>
<table width="780" border="0" align="center" cellpadding="0" cellspacing="0" bgcolor="#FFFFFF">
<tr>
<td>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td>


Another option to doing this is to put the advertising codes in the footer as being in the header, it may slow page load down.

Good luck.