NotifyIcon is not implemented in WPF as it is in Forms, but you can still use the Windows Form NotifyIcon, it resides in the System.Windows.Forms namspace.
Take a look at these tutorials, they might cover your needs:
Simple solution, directly using NotifyIcon:
http://www.abhisheksur.com/2012/08/notifyicon-with-wpf-applications.html
More advanced solution, new library based on NotifyIcon with more features:
http://www.codeproject.com/Articles/36468/WPF-NotifyIcon
More info about NotifyIcon can be found here:
http://msdn.microsoft.com/en-us/library/system.windows.forms.notifyicon.aspx