alright now firstly with corporate you need to place the ad near the top of the page so it can be seen with out scrolling at stipulated in x10hostings tos.
You'll need to edit one file, and you can edit the file by using an FTP client, or FileManager (from cPanel). Go to the phpBB folder, then go to the templates folder, and then to the folder your template is using. Edit the file overall_header.tpl.
Now just replace:
Code:
<html dir="{S_CONTENT_DIRECTION}">
with this:
Code:
<div align="center"><script type="text/javascript" src="http://x10hosting.com/adserve.js?corporate"></script></div>
<html dir="{S_CONTENT_DIRECTION}">
Then save the file, and that's it, you'll have the ad working in every page.
these instructions are straight from the how to insert ads post
http://forums.x10hosting.com/free-hosting/22505-how-insert-ads.html
i hope this helps