I’ve been wondering and searching for ways to load an html page inside my Unity Webplayer Application build to GUITextures(plane/box) for displaying the content of the webpage), all I found was an idea to attach a link on buttons and being redirected to the html page on browsers.
Html files are just text files. Sure you can load them with the WWW class, but rendering the content on screen is what a web browser does and it requires a lot of coding. Maybe there are some c# libraries you could find that could help you with this but i doubt they’d be free and/or straightforward to integrate to Unity :-/