Why does Netscape 4 show the source my .shtml page?
Instead of showing the rendered html of a page making use of server-side includes, some browsers tend to show the raw html source instead. This is caused by a misconfigured server. The content-type of an html document is text/html, certain servers that haven't been configured properly send out the HTTP header with the Content-Type set to text/plain and this results in browsers displaying the html source instead of rendering it.
The fix is simple enough, just configure your webserver to return the content-type of text/html for your pages with an .shtml extension (or whatever extension you are using for server side includes).