You know, the easiest way to do this would be to use ".shtml".
Most servers support this, and it allow your "shtml" pages to easily include other pages.
Say you have "home.shtml". In it you might write:
<!-- #include file="header.html" -->
<!-- #include file="nav.html" -->
... etc. ...
Check with your ISP if they support SHMTL, but I will bet they do.
If you need a simple-minded demo I can make one.