Xitherun Wrote:I probably know nothing, but it seems like it'd be redundant to have multiple .html files that all have the 'banner' and sidebar, and only change the content.

That's typically what is done nowadays.  With most websites going dynamic, it's not that difficult either.
The problem with frames:
- navigating to a new page doesn't change the URL in the address bar, so a newbie wants to link someone to a particular page...
- issues with saving pages
- only part of the webpage scrolls (not typical behaviour these days)
- thing breaks if you open a link in a new tab

Xitherun Wrote:Can I have a div or table display an external .html file?

No, only frames can really do that (Javascript or server scripts don't count :P).