Does your browsr.cgi script redirect the user to the appropriate .shtml page? Or, does your script actually open the .shtml page and print the HTML code?

The web server program can only process server-side includes when reading a parsed HTML file. It cannot process SSI's in the HTML output from your CGI script (unless you are using Apache 2.0 with some cool new features -- which I have not had a chance to play with yet).