Hmmm... I was thinking of an entire CMS, but yours doesn't seem that complex ... How are your clients accessing the editor?? Is through a link you provide ??? If so, then create a function to replace that link so that it can pass an identifier for your pages ...
For example, create a script to loop through your HTML directory that will display anything that has the .html or .htm extension. For each of the page you loop through, set a identifier for it. Let's say, if your page is Home.html, then set a new variable, lets say page_name = the name of the file... This could be tricky if you have files with space in them, you will have to replace the spaces with %20, and sor forth with ' or " .... In that loop, create an edit link or button that will refer to all the identifiers you want for that page ... So the links i guess would be editor.asp?page_name=Home.html ... Set in your editor file the script to catch the page_name variable, whether it is in a form or a link you will have to use either a request.form or request.quertystring depending on how you want to pass your page_name variable ...
You will have to do the same with the Save function so it will know which page to save it to ...
This is of course based on my assumption of how the editor works when calling from files instead of DB content. I might be a bit off, but I am sure the general idea is the same ...