"Luckily, there is a solution to get rid of these advertisements and make Skype better (although it still has too many problems than the older versions).
1. Open-up the control panel.
2. Open-up "Network & Internet" then "Internet Options".
3. Go to the "Security" tab.
4. Click on the "Restricted Sites" icon, then the "Sites" button below it.
5. Type "https://apps.skype.com/" (without the quotes) into the text box and click "Add"
a. Type "g.msn.com" (without the quotes) into the text box and click "Add"
6. Close and apply the changes.
7. Restart Skype.
That's the relatively easy way to block them though may leave a blank "placeholder" behind...
The more advanced bit is as follows:
With Skype completely closed (click quit on it's icon in system tray).
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:
Change the 1 to 0 (zero). Mark the file as read only.
Relaunch Skype. Ad gone.
From a Skype community forum.
*** Has had some mixed results it seems though but may be worth a try.