MSN TV (originally known as WebTV) capabilities are pretty limited. It doesn't have a hard drive or run any standard operating system, so downloadable games are out. Also, it doesn't support Java, so the large number of Java-based games are also unplayable on WebTV.
For a listing of solitaires you can play, go to the WebTV Solitaires page.
Also, there is a great collection of WebTV-compatible card games at The House Of Cards, and WebTV-compatible board games at Board Game Central.
