To the best of my knowledge, HTML will not suffice for what you want. The best way to write the form input to a file (or a database) is a server-side scripting language like perl /cgi or better yet, php. HTML can't do what you want. Sorry. On that note, I don't know enough about perl or php to be able to help, but if you have a Moderator move this post to one of those forums, someone might be able to help. Good luck!
Chris