I found what seems to be a solution at http://community.skype.com/t5/Windows-desktop-client/how-to-turn-off-the-skype-update-notifications/td-p/903552/page/2 ...
1) Redownload the SkypeSetup.exe file for the current version of Skype you wish to use/have installed
2) Navigate to the temp folder with the SkypeSetup.exe that updates to the newest version every time you start Skype
3) Delete SkypeSetup.exe, and replace it with the setup file for the current version of Skype you desire
4) Before you start Skype again, make sure to right click the SkypeSetup.exe file you have planted in the Temp folder, check Read-only, and hit apply
-This locks the file from being updated by Skype when you start it, and also takes the place of the Setup file Skype tries to force you to download-
5) Start Skype