I\'m required to develop a simple Windows system tray desktop app to consume a .NET web service but I\'m proficient in PHP, and I have little background in desktop applications.
Keep it all in .NET. You can easily write a Windows Forms application to display a tray icon and display notifications as and when something happens in the web service (you'd probably need a timer to do the polling).
There are plenty of articles around that will show you how to do this. Here's one to get you started:
http://www.codeproject.com/Articles/290013/Formless-System-Tray-Application