Is it possible to call in html code from another html file?

[Deja Q]

This one is tricky.

I know how to link to external javascript files.

Ditto for CSS.

But I'd like to link to a html file from within another.

I'm developing a dropdown menu system that I'd like to reuse in all my pages that doesn't use frames (it can't work in frames anyway because the code revolves around hidden tables, div tags, and css that is backward compatible to Netscrape 4...)

And I'd prefer to edit one menu file, instead of going into 16 pages to change the menu. :-) (even 10 pages is awkward...)

Here's the website that will eventually have the menu (the menu graphics are up, but I haven't coded the menu yet so they're useless...) http://www.thermodynamic-online.com/mccoy/index.html

(if there is a way to do this, I have another website in dire need of an overhaul. It has over 100 separate pages, hence if this internal linking to another html file works, this would be of incredible service...)

Thanks!!