Personally I would advise against using iframes as they are going against many of the principles outlined in the book (and are generally old hat).
If you are using frames as a way to display common content accross all your pages such as menus/headers/footers you should look into using Master Pages (good explanation in the book).
If however you need some way of updating various content of your page asyncronously without fully posting the page back to the server I would suggest looking into AJAX (http://asp.net/learn/ajax/
You can achieve what you wish to do quite easily with partial page updates using an UpdatePanel. You can dynamically change the source for your panel at runtime.
Hope this helps.