This is the bottom line:
Corperate Accounts:
Your own ads must not be any bigger than that of the Corperate Banner used by X10.
Advanced Accounts:
Your own ads can be as big as you want them to be, as long as they do not draw attention away from the X10Ads you are using.
If you are on a advanced plan account you can place both sets of ad codes on your website, for both advanced and corperate. If you are on corperate you can only use the corperate ad code.
I hope that this clears up some of the things rasied here!
Regards,
Zenax