chun914,
Welcome to Apple Discussions.
Going forward rather than doing a "me too" it's better to create a new thread. When you say you download and install MSN, what exactly is MSN? You should see file extension like .app when it's in the downloads folder. What is that extension, that might give me a clue as to what it is.
Also go through the Mac 101 and Switch 101 URL's that were noted above and get yourself a book on Snow Leopard so you can begin learning. A book I like is
Robin Williams book, no not THAT Robin Williams! 🙂
Regards,
Roger