I answered a couple of certificate questions in the C# Windows Store applications forum that you all may find useful:
Provide Client side certificate:
Include Server certificate in manifest so application cantrust an non-trusted or self-issued server certificate:
Great video describing SelfSigned certs and embedding it in an app:
http://channel9.msdn.com/Events/Build/2012/3-127 See at 0:36 - 0:42 for the SSL part.