I'm not entirely clear about what you're asking for, but I think you want a request for a .htm page to transparently fire a cgi script which generates the page. You can set that up with Apache's mod_rewrite. In .htaccess put:

RewriteEngine  on
RewriteBase    /~quux/
RewriteRule    ^page1\.htm$  a.cgi  [T=application/x-httpd-cgi]
[download]

(Adapted from the URL Rewriting Guide in the Apache manual.)

I can see that you might be asking about something entirely different, maybe something about displaying a link. If so, please clarify.