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Answer by Rex M
What you are describing is accomplished using frames, and is in this enlightened age generally considered by experts of design and usability to be a “bad thing”. I highly advocate rethinking your ambitions for your site. Notice that sites such as Yahoo and Amazon, who spend millions per year on research and development, do not use frames. Why, then, would it make sense for you to do so?

However, if you feel you must totally use them, you can learn about them here: http://www.w3schools.com/html/html_frames.asp

Some users might recommend AJAX, but usability research is showing that it is also inappropriate for a web site situation. Users anticipate web sites to be collections of complete pages (as noted in the Jakob Nielsen article linked to by Mr. Tark), and to behave as such. If you are developing a web site, then stick with the pages paradigm. However, if you are developing a web *application*, then AJAX very well might be appropriate for your needs. Users anticipate web applications, such as Yahoo! Mail, to be static and behave more like a desktop program, wherein relevant portions of the screen are updated as needed, while retaining the say of the rest of the UI.

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