Arduino communicates with MSN Messenger?

Can anyone give me hints how to communicate Instant Messenger(like MSN, Skype,...) with Arduino?

The MSN protocol is I think (too) complex to be handled by an arduino. That said you could use the Arduino to emulate a keyboard - see playground articles - to send info from sensors in the front window of a PC. Reading the reply's from MSN is far more complex as one needs to intercept the primary windows event loop to catch the characters sent to the MSN window. That kind of tooling is often detected by virsuscanners as malware.

What is the goal that you want accomplish, is MSN the right tool?

Thanks for your answer!
I would like to get sensor’s response(eg. temperature,…) via MSN from arduino, or I can remotely control arduino with LED lamp via MSN. I don’t need a keyboard attached. Is it possible to realize it?

Is it possible to realize it?

Unlikely.

You'd be much better off setting up a webpage or something for this.