This is a short example of creating a WPF application that links to Skype using Skype4COM. You can call people on your contact list, search for new contacts and view incoming chat messages. It includes a fully skinnable interface (edit theme.xaml)
I've also bundled the required Skype4COM DLL, but you can grab the original from http://dev.skype.com/accessories/skype4com
Requires the free Microsoft Visual Studio Express 2012 (Desktop) edition.