Another site you might want to visit allows you to see how your web page would look if certain features were unavailable, such as frames, some colors, Javascript and the like: www.delorie.com/web/wpbcv.html.
WebTV lets a viewer access the World Wide Web via a standard television screen which is very different than a computer monitor. The The WebTV devlopers' site has a lot of guidance for those developing web pages for the WebTV audience.
You need to test using different sized monitors, Macs and PCs, and Netscape and Internet Explorer. Also, play with the font sizes on the browser to make sure your pages looks reasonable under various settings.