Due to the way this is coded you can add the banner display area first without it having any impact upon your site until someone adds a banner via the account page.

Firstly add the following code where you wish the banners to be displayed:

<script type="text/javascript">
/*<![CDATA[*/
n = 0;
r = new Array();
[start:members]
[if:banner]
r[n++] = '<img src="[banner]" style="width: [bwidth]px; height: [bheight]px; cursor: pointer; border: 0;" alt="Advertise" onclick="javascript:window.open(\'[link]\');" />';
[endif:banner]
[stop:members]
i=Math.floor(Math.random() * n);
if (r[i] == undefined) {
document.write('');
} else {
document.write(r[i]);
}
/*]]>*/
</script>

Then add the following code to the top of your account page:

<script type="text/javascript">
/*<![CDATA[*/
function check_banner(){
var height_constraint = 75;
var width_constraint = 500;

if((document.getElementById('bheight').value > height_constraint) || (document.getElementById('bwidth').value > width_constraint))
{
document.getElementById('bheight').value=60;
document.getElementById('bwidth').value=468;
document.getElementById('bheight').focus();
document.getElementById('bheight').focus();
alert('Banner size too big. Size set to 468x60.');
}
if((document.getElementById('bheight').value=="") || (document.getElementById('bwidth').value==""))
{
document.getElementById('bheight').value=0;
document.getElementById('bwidth').value=0;
document.getElementById('bheight').focus();
document.getElementById('bheight').focus();
alert('Banner size not entered. Size set to 0x0.');
}
}
/*]]>*/
</script>

Finally add this last code where you wish the entry to be on your account page:

<tr>
<td class="tableHeader"> Banner Image:</td>
<td> <input type="text" name="banner" value="[banner]" /></td>
</tr>
<tr>
<td class="tableHeader"> Banner Size:</td>
<td> Width: <input type="text" id="bwidth" name="bwidth" value="[bwidth]" size="5" maxlength="3" />
Height: <input type="text" id="bheight" name="bheight" value="[bheight]" size="5" maxlength="3" /></td>
</tr>
<tr>
<td class="tableHeader"> Banner Link:</td>
<td> <input type="text" name="link" value="[link]" /></td>
</tr>