1.
Easy enough to hide the ad completely.
First block apps.skype.com like tutorial says.
With Skype completely closed (click quit on it's icon in system tray).

2.
Go to:
%AppData%\Skype\
Click on the folder that is the same name as your Skype User name.
Open the config.xml in your fav txt editor and change this line:
<AdvertPlaceholder>1</AdvertPlaceholder>
Change the 1 to 0 (zero). Mark the file as read only.
Relaunch Skype.