The tab mix plus extension for Firefox, among others, gives you auto-reload ability.
I'm not exactly sure what you mean by your second question. If you don't want to re-read old stuff, then just don't read it.
But if you really mean only having the browser refresh the parts of the page that have changed, then no, it's not possible with regular html pages. The documents need to be downloaded in full in order to be parsed.
But a big part of "Web 2.0" technology is using things like ajax, javascript, dhtml, etc., to create pages that can do that. The pages and the server that provides them have to be programmed for it though.