I am developing an application in php. I need to display a notification message on windows taskbar. So please help me...How to do it using php.
With PHP, your domain is the web browser. You can display a message in the browser or in a pop up window. You can't connect to the operating system.
Probably PHPGTK can help you. But your question smells a bit, because as Sohnee mentioned PHP is made for creating web pages or things which are highly connected to the web.
However, it could help us if you provide much more information what you do, why you do it, and so on...
You could change the window title using ajax to display a message in the taskbar. That's as far as you can go using a webapp i think.
You might want to look for a Growl library. On Widows it would require some additional software. Google turns up:
With C# for .NET you can easily write a notifier application which resides in the tray.
I just have written an XML based notifier application which communicates (XML data transfer) with a server that runs php. The IDE comes with a sample notifier application. If you are familiar with c# then go and get it.
It's open source Goto SharpDevelopment IDE
What you can do, is develop a program that does this in another language, and then call it via system() in PHP.
Note that the notification will only pop up on the server. Since no actual PHP code is run on the client's machine.