I would certainly take a close look at using Template Toolkit as your template engine. It enables (encourages) the use of modular templates. So, you can have a "sidebar" template, a "navbar" template, and a "body" template; the first two would be "included" on every page while the third would vary based on what content you were serving.

Capitalizing on the template engine allows you to make changes to the presentation (even drastic changes) without changing any underlying data. Storing HTML as your "content" has a significant downside. If you ever want to change the content, which the client is probably making available as something other than HTML, you have to regenerate the content that goes to the site. With a templating solution, the content is stored in a raw form and just plugged into the template appropriately.

I would also agree with the first poster that CGI::Application is a good stepping-off point for developing such a site. I would add that I have found Catalyst useful in this regard as well. The two accomplish the same task, but take very different approaches. There are other web frameworks out there, as well.

Sean