How to use server-side includes
How to use server-side includes with Blogger
Took a while to find this, but this page gives details about using server side includes to make blogs look nice on my site. It's pretty deep, but kind of fun to figure out. The hard thing is getting archives to work correctly.
The term 'includes' covers a simple web server technology that allows you to include, or insert, a second file into an existing file and is popular for many reasons. It allows you to make consistent header, footer, or entire web page templates that run from a single location, making updates and changes to that template very easy. Taking most of your HTML out of your Blogger template also allows you to separate your content (in Blogger) from your presentation (in your template file). Includes are easy to implement, but do present minor challenges for blogs, including archiving and permanent links.
Once you've got basic includes working, you'll probably want to get archives running off the same template file. You might also want to add permanent links as well as a second or third Blogger-powered page to your site that uses the same template. This can be done by adding a few more lines of code around the includes code you added earlier. Basically, you'll be passing along the name of the includes through the URL query string, so instead going to your blog's main page at http://yourserver.com/index.html your archives might be at http://yourserver.com/index.html?p=archive.html.