This is an excellent idea. In fact it's be done before (at least 3X in fact).

You are looking for a templating system. Here are the 3 most popular that I know of.

Template Toolkit - My personal favorite runs on Win32 and *nix, also does other templating besides HTML

HTML::Mason - also very good - requires Apache

HTML::Template - also very good

grep

Mynd you, mønk bites Kan be pretti nasti...