How would I go about doing this?

I would like to include code from a seperate file into an html document.  Specifically, like having a variable that would count as anything written in a seperate noted document.

example:

<cover.txt>
My opinion of <title.txt> is <review.txt>.
I give it <rating.txt> and if you like it I reccomend that you view <recommendations.txt>.

Please view my other reviews
(drop down menu code)
<../../selections.txt>
(/drop down menu code)

and each of these .txt files, or whatever they are, would contain the html which it would include in the pages.

The goal of this being to update multiple pages because they all depend on one file.

So please, how do you do this?  I hunger for knowledge, and don't know how to word my google searches.

What you are searching for is a Database Managing System. This is best for you, since you obviously don't know how to PHP, JSP, or server-side programming. My advice is: Read SICP, read some tutorials on database-based web sites, read SICP again for decontamination (since web site development is dirty as shit).

Enjoy developing!