<p>I know you can do a trick of putting an HTML element on top of a Silverlight app, but that will not work full screen.  Is there anyway to show an html page inside a Silverlight application?</p>

The answer is, you can't. At least right now you can't - in the future it might be added but that's certainly not going to occur for a number of years (2.0 RTW was released today).
However, this link may be of some interest:
http://blogs.msdn.com/delay/archive/2007/09/10/bringing-a-bit-of-html-to-silverlight-htmltextblock-makes-rich-text-display-easy.aspx
It basically parses some "HTML text" and displays it as it can in a text block. Works for simple stuff, but may not be as complex as you need.