Tweaking comments popup in 1.5

I have uncommented “comments_popup_script()” in my customized theme header (a modified version of the “classic” theme). I do get the popup with a miniature version of the index page, so the basic mechanism seems to be working.

How do I instruct it now to load instead a customized popup page?

I tried passing the name of the customized page, “comments-popup.php”, to the function, comments_popup_script(500,700,’comments-popup.php’), but all I get is an error message:

The requested URL /[path to the blog root]/comments-popup.php was not found on this server. It appears that it does not know the correct path, i.e. …/wp-content/themes/mytheme/

Am I missing something? I did a search of the support area, and while some people mention the popup, nobody seems to be using a customized file different from the index. Also, codex.www.ads-software.com appears to be non-functional: it redirects to www.ads-software.com so all the references to it are unaccessible.

Thanks,

Pierre