When you create a form to be used by a web server that supports FrontPage Server Extensions (for example Microsoft IIS or Apache), follow these steps:
Place it on an HTTPS:-site and password protect it. How to password protect depends on which type of webserver you are using.
By enabling compression, the amount of data you download will be 1/10. All modern browser support compression.
If you are using SpreadsheetConverter/ExcelEverywhere to HTML and want your users to login before they can use the calculator, the solution is to use the authentication of the web server to handle this. Both Internet Information Server (IIS) and Apache handles this.
If you use IIS, you can create normal Windows users and deny guest access to your web server.
If you use Apache, here is an article describing it: Protect Web sites with Apache Server’s HTTP authentication system. Alternatively, you can program the authentication yourself. Secure your Web pages with custom authentication Or, you can use ASP.NET’s form authentication. A simple solution is to store name + password in web.config. ASP.NET Form Authenticiation tutorial The SpreadsheetServer also handles logins.