Into template file, you can use next command:
<TMPL_INCLUDE NAME="file-name.html">
When you output this template, file - "file-name.html" will be included into your document...
http://html-template.sourceforge.net/ - download this module.
http://html-template.sourceforge.net/article.html - docs
example from me:
template.html:
file-name.html
script.cgi
Try it. It's very usefull.