Just to add one more comment about Server Side Includes.
If you tried the code I posted earlier and it did not include your .html file as expected, it is probably due to your server's configuration.
Code:
<!--#include file="includes/filename.html" -->
So if the above code doesn't include your .html files properly, then you'll have to rename your .html files to .shtml.
You would then use the following:
Code:
<!--#include file="includes/filename.shtml" -->
The reason why the .shtml extension is often required is so that the server doesn't waste time and resources searching through every .html file for an include statement. By giving a .shtml extension, the server will only expect an include to possibly occur in that filetype.
Note: You can use either .shtml or .shtm.